All Solutions
Section 4-6: Transformations of Exponential Functions
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
Transformation & Description \ hline
$y=f(x)+c$ & begin{tabular}[c]{@{}l@{}}vertical translation of\ $c$ units upwardend{tabular} \ hline
$y=f(x+d)$ & begin{tabular}[c]{@{}l@{}}horizontal translation of $d$ units\ to the leftend{tabular} \ hline
$y=acdot f(x)$ & begin{tabular}[c]{@{}l@{}}vertical stretching by a factor of $a$end{tabular} \ hline
$y=f(kx)$ & begin{tabular}[c]{@{}l@{}}horizontal compression by $dfrac{1}{|k|}$end{tabular} \ hline
$y=-f(x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in\ the $x$-axisend{tabular} \ hline
$y=f(-x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in \ the $y$-axisend{tabular} \ hline
end{tabular}
end{table}
a) $g(x)=3^x+3=f(x)+3implies$ vertical translation 3 units upward
b) $g(x)=3^{x+3}=f(x+3)implies$ horizontal translation 3 units to the left
c) $g(x)=dfrac{1}{3}(3^x)=dfrac{1}{3}f(x)implies$ vertical compression by factor of $3$ ($y$-values decreased by $dfrac{1}{3}$
d) $g(x)=3^{frac{x}{3}}=fleft(dfrac{x}{3}right)implies$ horizontal stretching by a factor of $3$
b) horizontal translation 3 units to the left
c) vertical compression by a factor of 3
d) horizontal stretching by a factor of $3$
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
Transformation & Description \ hline
$y=f(x)+c$ & begin{tabular}[c]{@{}l@{}}vertical translation of\ $c$ units upwardend{tabular} \ hline
$y=f(x+d)$ & begin{tabular}[c]{@{}l@{}}horizontal translation of $d$ units\ to the leftend{tabular} \ hline
$y=acdot f(x)$ & begin{tabular}[c]{@{}l@{}}vertical stretching by a factor of $a$end{tabular} \ hline
$y=f(kx)$ & begin{tabular}[c]{@{}l@{}}horizontal compression by $dfrac{1}{|k|}$end{tabular} \ hline
$y=-f(x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in\ the $x$-axisend{tabular} \ hline
$y=f(-x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in \ the $y$-axisend{tabular} \ hline
end{tabular}
end{table}
(1) horizontal translation to the left $implies 4^{x+1}$
(2) vertical stretching by a factor of 3 $implies 3(4^{x+1})$
(3) reflecting in the $x$-axis $implies -3(4^{x+1})$
(1) horizontal compression by a factor of $dfrac{1}{2}implies left(dfrac{1}{2}right)^{2x}$
(2) vertical stretching by a factor of $2implies 2left(dfrac{1}{2}right)^{2x}$
(3) vertical translation 3 units upward $implies 2left(dfrac{1}{2}right)^{2x}+3$
(1) horizontal translation 4 units to the right $implies 0.5^{x-4}$
(2) vertical stretching by a factor of $7implies 7(0.5^{x-4})$
(3) vertical translation 1 unit downwards $implies 7(0.5^{x-4})-1$
Base function: $5^x$
(1) horizontal compression by a factor of $dfrac{1}{3}implies 5^{3x}$
(2) horizontal translation 2 units to the right $implies5^{3(x-2)}$
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
a) & begin{tabular}[c]{@{}l@{}}Base function: $4^x$\ (1) horizontal translation to the left $implies 4^{x+1}$\ (2) vertical stretching by a factor of 3 $implies 3(4^{x+1})$\ (3) reflecting in the $x$-axis $implies -3(4^{x+1})$end{tabular} \ hline
b) & begin{tabular}[c]{@{}l@{}}Base function: $left(frac{1}{2}right)^x$\ (1) horizontal compression by a factor of $frac{1}{2}implies left(frac{1}{2}right)^{2x}$\ (2) vertical stretching by a factor of $2implies 2left(frac{1}{2}right)^{2x}$\ (3) vertical translation 3 units upward $implies 2left(frac{1}{2}right)^{2x}+3$end{tabular} \ hline
c) & begin{tabular}[c]{@{}l@{}}Base function: $(0.5)^x$\ (1) horizontal translation 4 units to the right $implies 0.5^{x-4}$\ (2) vertical stretching by a factor of $7implies 7(0.5^{x-4})$\ (3) vertical translation 1 unit downwards $implies 7(0.5^{x-4})-1$end{tabular} \ hline
d) & begin{tabular}[c]{@{}l@{}}$h(x)=5^{3x-6}=5^{3(x-2)}$\ Base function: $5^x$\ (1) horizontal compression by a factor of $dfrac{1}{3}implies 5^{3x}$\ (2) horizontal translation 2 units to the right $implies5^{3(x-2)}$end{tabular} \ hline
end{tabular}
end{table}
$y$-intercept: value of $y$ when $x=0$
asymptote: $y=c$
domain = ${ xinbold{R}}$
$$
{text{range = }}left{ {begin{array}{c}
{left{ {y in {mathbf{R}};|;y > c{text{ }}} right}{text{ if }}a > 0,,,} \
{left{ {y in {mathbf{R}};|;y < c{text{ }}} right}{text{ if }}a < 0}
end{array}} right.
$$
defarraystretch{2.2}%
begin{tabular}{|l|l|l|l|l|}
hline
Function & $y$-intercept & Asymptote & Domain & Range \ hline
$y=3^x+3$ & $4$ & $y=3$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>3}$ \ hline
$y=3^{x+3}$ & $27$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
$y=dfrac{1}{3}(3^x)$ & $dfrac{1}{3}$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
$y=3^{frac{x}{3}}$ & $1$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
$y=-3(4^{x+1})$ & $-12$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y3}$ \ hline
$y=7(0.5^{x-4})-1$ & 111 & $y=-1$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>-1}$ \ hline
$y=5^{3x-6}$ & $6.4times10^{-5}$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
end{tabular}
end{table}
defarraystretch{1.5}%
begin{tabular}{|l|l|l|l|l|}
hline
Function & $y$-intercept & Asymptote & Domain & Range \ hline
$y=3^x+3$ & $4$ & $y=3$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>3}$ \ hline
$y=3^{x+3}$ & $27$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
$y=frac{1}{3}(3^x)$ & $frac{1}{3}$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
$y=3^{frac{x}{3}}$ & $1$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
$y=-3(4^{x+1})$ & $-12$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y3}$ \ hline
$y=7(0.5^{x-4})-1$ & 111 & $y=-1$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>-1}$ \ hline
$y=5^{3x-6}$ & $6.4times10^{-5}$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>0}$ \ hline
end{tabular}
end{table}
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
Transformation & Description \ hline
$y=f(x)+c$ & begin{tabular}[c]{@{}l@{}}vertical translation of\ $c$ units upwardend{tabular} \ hline
$y=f(x+d)$ & begin{tabular}[c]{@{}l@{}}horizontal translation of $d$ units\ to the leftend{tabular} \ hline
$y=acdot f(x)$ & begin{tabular}[c]{@{}l@{}}vertical stretching by a factor of $a$end{tabular} \ hline
$y=f(kx)$ & begin{tabular}[c]{@{}l@{}}horizontal compression by $dfrac{1}{|k|}$end{tabular} \ hline
$y=-f(x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in\ the $x$-axisend{tabular} \ hline
$y=f(-x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in \ the $y$-axisend{tabular} \ hline
end{tabular}
end{table}
a) Horizontal compression by a factor of $dfrac{1}{|k|} = frac 1 2$ and then reflecting in the $x$-axis and reflection about $y$ axis.
b) Horizontal translation 3 units to the right, reflecting in the $y$-axis and then vertical stretching by a factor of 5.
c) $g(x)=-4left(dfrac{1}{2}right)^{3x+9}-6=-4left(dfrac{1}{2}right)^{3(x+3)}-6$
Horizontal translation 3 units to the left, horizontal compression by a factor of $dfrac{1}{3}$, vertical stretching by a factor of 4, reflecting in the $x$-axis, and vertical translation 6 units downward.
b) Horizontal translation 3 units to the right, reflecting in the $y$-axis and then vertical stretching by a factor of 5.
c) Horizontal translation 3 units to the left, horizontal compression by a factor of $dfrac{1}{3}$, vertical stretching by a factor of 4, reflecting in the $x$-axis, and vertical translation 6 units downward.
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
Transformation & Description \ hline
$y=f(x)+c$ & begin{tabular}[c]{@{}l@{}}vertical translation of\ $c$ units upwardend{tabular} \ hline
$y=f(x+d)$ & begin{tabular}[c]{@{}l@{}}horizontal translation of $d$ units\ to the leftend{tabular} \ hline
$y=acdot f(x)$ & begin{tabular}[c]{@{}l@{}}vertical stretching by a factor of $a$end{tabular} \ hline
$y=f(kx)$ & begin{tabular}[c]{@{}l@{}}horizontal compression by $dfrac{1}{|k|}$end{tabular} \ hline
$y=-f(x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in\ the $x$-axisend{tabular} \ hline
$y=f(-x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in \ the $y$-axisend{tabular} \ hline
end{tabular}
end{table}
For a general exponential function $g(x)=acdot b^{k(x-d)}+c$\\
$y$-intercept: value of $y$ when $x=0$ \\
asymptote: $y=c$\\
domain = ${ xinbold{R}}$\\
${text{range = }}left{ {begin{array}{*{20}{c}}
{left{ {y in {mathbf{R}};|;y > c{text{ }}} right}{text{ if }}a > 0,,,} \
{left{ {y in {mathbf{R}};|;y < c{text{ }}} right}{text{ if }}a < 0}
end{array}} right.$
a) reflecting the function in the $y$-axis, vertical stretching by a factor of $0.5$ and vertical translation 2 units upward.
$g(x)=0.5(4^{-x})+2$
$y$-intercept: $y=0.5(4^{0})+2=0.5(1)+2=2.5$
asymptote: $y=2$
domain: ${ xinbold{R}}$
range: ${ yinbold{R};|;y>2}$
Horizontal stretching by a factor of $dfrac{1}{0.25}=4$, horizontal translation 4 units to the left, reflecting in the $x$-axis, and vertical translation 1 unit downward.
$h(x)=-(4^{0.25x+1})-1$
$y$-intercept: $y=-4^{0+1}-1=-5$
asymptote: $y=-1$
domain = ${ xinbold{R}}$
range = ${ yinbold{R};|;y<-1}$
Horizontal compression by a factor of $dfrac{1}{2}$, horizontal translation 3 units to the right, vertical stretching by a factor of 2, reflection in the $x$-axis.
$g(x)=-2(4^{2x-6})$
$y$-axis: $y=-2(4^{2(0)-6})=-2(4^{-6})=dfrac{-2}{4^6}=-dfrac{1}{2048}$
asymptote: $y=0$
domain: ${ xinbold{R}}$
range: ${ yinbold{R};|;y<0}$
Horizontal stretching by a factor of $dfrac{1}{0.5}=2$, reflecting in the $y$-axis, horizontal translation 1 unit to the right.
$h(x)=4^{-0.5x+1}$
$y$-intercept: $y=4^{-0.5(0)+1}=4$
asymptote: $y=0$
domain: ${ xinbold{R};}$
range: ${ yinbold{R};|;y>0}$
defarraystretch{1.7}%
begin{tabular}{|l|l|l|l|l|}
hline
Function & $y$-intercept & Asymptote & Domain & Range \ hline
a) $g(x)=0.5(4^{-x})+2$ & $2.5$ & $y=2$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y>2}$ \ hline
b) $h(x)=-4^{0.25x+1}-1$ & $-5$ & $y=-1$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y<-1}$ \ hline
c) $g(x)=-2(4^{2x-6})$ & $-frac{1}{2048}$ & $y=0$ & ${ xinbold{R}}$ & ${ yinbold{R};|;y0}$ \ hline
end{tabular}
end{table}
$g(x)=3^{2x}=9^x$
Both functions have the same $y$-intercept $(0,1)$, asymptote $y=0$, domain ${xinbold{R}}$ and range ${ yinbold{R};|;y>0}$
Since $g(x)$ has greater base, it increases faster than $f(x)$.
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
Transformation & Description \ hline
$y=f(x)+c$ & begin{tabular}[c]{@{}l@{}}vertical translation of\ $c$ units upwardend{tabular} \ hline
$y=f(x+d)$ & begin{tabular}[c]{@{}l@{}}horizontal translation of $d$ units\ to the leftend{tabular} \ hline
$y=acdot f(x)$ & begin{tabular}[c]{@{}l@{}}vertical stretching by a factor of $a$end{tabular} \ hline
$y=f(kx)$ & begin{tabular}[c]{@{}l@{}}horizontal compression by $dfrac{1}{|k|}$end{tabular} \ hline
$y=-f(x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in\ the $x$-axisend{tabular} \ hline
$y=f(-x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in \ the $y$-axisend{tabular} \ hline
end{tabular}
end{table}
For a general exponential function $g(x)=acdot b^{k(x-d)}+c$\\
$y$-intercept: value of $y$ when $x=0$ \\
asymptote: $y=c$\\
domain = ${ xinbold{R}}$\\
${text{range = }}left{ {begin{array}{*{20}{c}}
{left{ {y in {mathbf{R}};|;y > c{text{ }}} right}{text{ if }}a > 0} \
{left{ {y in {mathbf{R}};|;y < c{text{ }}} right}{text{ if }}a < 0}
end{array}} right.$
horizontal compression by a factor of $30implies left(dfrac{1}{2}right)^{frac{t}{30}}$
vertical stretching by a factor of $80implies 80left(dfrac{1}{2}right)^{frac{t}{30}}$
vertical translation 20 units upward $implies T(t)=80left(dfrac{1}{2}right)^{frac{t}{30}}+20$
The asymptote $y=20$ is the lower limit of the liquid temperature, in other words, the temperature of the liquid would approach $20^circ$ as time increases.
$N(t)=N_02^{frac{t}{3}}$
where $N_0$ is the population at $t=0$
a) If doubling time is changed to $9$ h, the new function would be $F(t)=N_02^{frac{t}{9}}$. Notice that the exponent is smaller, so the graph would rise slower than the original function. This also corresponds to horizontal stretching by a factor of 3.
b) The domain is ${ tinbold{R};|;tgeq0}$. The domain is the period of time at which the yeast cells are allowed to grow which can’t be negative.
The range is ${ Ninbold{R};|;N>N_0}$ because $N(t)$ is an increasing function so the population cannot be lower than the initial population $N_0$.
b) domain = ${ tinbold{R};|;tgeq 0}$
range = ${ Ninbold{R};|;N>N_0}$
i.e. remains same
a) $f(x)=-left(dfrac{1}{4}right)^{-x}+3=-(4)^x+3$
The graph of $y=4^x$ lies above $x$-axis and increases from left to right.
$y=-4^x$ is reflected in the $x$-axis, so the function is now below $x$-axis and decreases from left to right.
$y=-4^x+3$ is a vertical translation 3 units upward so the $y$-intercept must be $-(4^0)+3=-1+3=2$
The graph that satisfies this is option (iii)
The graph of $y=4^x$ lies above $x$-axis and increases from left to right.
The graph of $y=4^{-x}$ is reflected in the $y$-axis so the graph is still above $x$-axis but is now decreasing from the left to right.
The graph of $y=4^{-x}+3$ is vertically translated 3 units upward so the $y$-intercept must be $4^{-0}+3=4$
The graph that satisfies this is option (ii)
The graph of $y=left(frac{5}{4}right)^x$ lies above $x$-axis and increasing from left to right.
The graph of $y=left(frac{5}{4}right)^{-x}$ is reflected in the $y$-axis so it’s still above $x$-axis but decreasing from left to right.
The graph of $y=-left(frac{5}{4}right)^{-x}$ is reflected in the $x$-axis so now it is below $x$-axis and increasing from left to right.
The graph is then translated 3 units upward so the $y$-intercept must be $-left(frac{5}{4}right)^{-0}+3=-1+3=2$
The graph that satisfies this is option (iv)
b) (ii)
c) (iv)
d) (i)
Now, observe that the graph passes through $(2,-10)$
If we use $x=2$, $y=-2^{x}+6=-2^{2}+6=2neq -10$ which implies that there must be horizontal stretching/compression so it must be of the form $y=-2^{kx}+6$
Substitute the point $(2,-10)$ to find $k$
$-10=-2^{k(2)}+6$
$2^{2k}=16$
$2^{2k}=2^{4}$
$2k=4$
$k=2$
Therefore, the equation is
$$
y=-2^{2x}+6
$$
$y=2^{-(x+3)}-2$
b) $y=2^{-(x+3)}-2$
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
Transformation & Description \ hline
$y=f(x)+c$ & begin{tabular}[c]{@{}l@{}}vertical translation of\ $c$ units upwardend{tabular} \ hline
$y=f(x+d)$ & begin{tabular}[c]{@{}l@{}}horizontal translation of $d$ units\ to the leftend{tabular} \ hline
$y=acdot f(x)$ & begin{tabular}[c]{@{}l@{}}vertical stretching by a factor of $a$end{tabular} \ hline
$y=f(kx)$ & begin{tabular}[c]{@{}l@{}}horizontal compression by $dfrac{1}{|k|}$end{tabular} \ hline
$y=-f(x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in\ the $x$-axisend{tabular} \ hline
$y=f(-x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in \ the $y$-axisend{tabular} \ hline
end{tabular}
end{table}
$f(x)=2^{x+1}+5$ $implies$ $g(x)=dfrac{1}{4}(2^x)$
(1) Vertical translation 5 units downward
$f(x)-5implies y=2^{x+1}$
(2) Horizontal translation 1 unit to the right
$f(x-1)-5 implies y=2^{x}$
(3) Vertical compression by a factor of $dfrac{1}{4}$
$$
dfrac{1}{4}[f(x-1)-5] implies g(x)=dfrac{1}{4}(2^x)
$$
(2) horizontal translation 1 unit to the right
(3) vertical compression by a factor of $frac{1}{4}$
defarraystretch{1.5}%
begin{tabular}{|l|l|}
hline
Transformation & Description \ hline
$y=f(x)+c$ & begin{tabular}[c]{@{}l@{}}vertical translation of\ $c$ units upwardend{tabular} \ hline
$y=f(x+d)$ & begin{tabular}[c]{@{}l@{}}horizontal translation of $d$ units\ to the leftend{tabular} \ hline
$y=acdot f(x)$ & begin{tabular}[c]{@{}l@{}}vertical stretching by a factor of $a$end{tabular} \ hline
$y=f(kx)$ & begin{tabular}[c]{@{}l@{}}horizontal compression by $dfrac{1}{|k|}$end{tabular} \ hline
$y=-f(x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in\ the $x$-axisend{tabular} \ hline
$y=f(-x)$ & begin{tabular}[c]{@{}l@{}}reflecting the function in \ the $y$-axisend{tabular} \ hline
end{tabular}
end{table}
to obtain $y=2^{-x}=dfrac{1}{2^x}$
1) Reflect in the $y$-axis to obtain $y=2^{-x}=dfrac{1}{2^x}$
2) Reflect in the $x$-axis to obtain $y=dfrac{-1}{2^x}$
3) Vertically stretch by a factor of 3 to obtain $y=dfrac{-3}{2^x}$
4) Translate 2 units to the left and 1 unit downwards $y=dfrac{-3}{2^{x+2}}-1$
$g(x)=4-2left( dfrac{1}{3}right)^{-0.5x+1}=4-2(3^{-1})^{-0.5x+1}=4-2(3^{0.5x-1})$
$$
g(x)=4-2left(3^{0.5(x-2)}right)
$$
(2) Horizontally compress by a factor of $dfrac{1}{0.5}=2$ to obtain $y=-3^{0.5x}$
(3) Vertically stretch by a factor of 2 to obtain $y=-2left(3^{0.5x}right)$
(4) Translate 2 units to the right and 4 units upward to obtain
$y=-2(3)^{0.5(x-2)}+4$
*Note that if we used $y=left(dfrac{1}{3}right)^x$ instead of $y=3^x$ as the base function, you need to reflect in the $y$-axis, that is, change $f(x)$ to $f(-x)$.
(2) Horizontally compress by a factor of $dfrac{1}{0.5}=2$ to obtain $y=-3^{0.5x}$
(3) Vertically stretch by a factor of 2 to obtain $y=-2left(3^{0.5x}right)$
(4) Translate 2 units to the right and 4 units upward to obtain
$y=-2(3)^{0.5(x-2)}+4$ which is just the same as $y=-2left(dfrac{1}{3}right)^{-0.5(x-2)}+4$
$m(x)=-left(dfrac{3}{2}right)^{2x-2}$ to $n(x)=-left(dfrac{9}{4}right)^{-x+1}+2$
Note that they have different base function so we need to rewrite $m(x)$ such that it has a base of $dfrac{9}{4}$
$m(x)=-left[left(dfrac{3}{2}right)^2right]^{2x-2}$
$m(x)=-left(dfrac{9}{4}right)^{frac{2x-2}{2}}$
$m(x)=-left(dfrac{9}{4}right)^{x-1}$
Thus, this transformation simplifies as
$$
m(x)=-left(dfrac{9}{4}right)^{x-1} text{ to } n(x)=-left(dfrac{9}{4}right)^{-(x-1)}+2
$$
(1) Reflect in the $y$-axis to obtain $y=-left(dfrac{9}{4}right)^{-(x-1)}=-left(dfrac{9}{4}right)^{-x+1}$
(2) Vertically translate 2 units upward to obtain $n(x)=-left(dfrac{9}{4}right)^{-x+1}+2$
Note that no vertical or horizontal scaling are needed.
(2) vertically translate 2 units upward