All Solutions
Section 9-5: Composition of Functions
$g(0)=1-0^2=1$
$f(g(0))=f(1)=2(1)-3=2-3=-1$
#### (b)
$f(4)=2(4)-3=8-3=5$
$g(f(4))=g(5)=1-5^2=1-25=-24$
#### (c)
$g(-8)=1-(-8)^2=1-64=-63$
$(fcirc g)(-8)=f(-63)=2(-63)-3=-126-3=-129$
#### (d)
$gleft( dfrac{1}{2}right)=1-left(dfrac{1}{2} right)^2=1-dfrac{1}{4}=dfrac{3}{4}$
$(g circ g)left(dfrac{1}{2} right)=gleft(dfrac{3}{4} right)=1-left( dfrac{3}{4}right)^2=1-dfrac{9}{16}=dfrac{7}{16}$
#### (e)
$(f circ f^{-1})(1)=1$
#### (f)
$g(2)=1-2^2=1-4=-3$
$(g circ g)(2)=g(-3)=1-(-3)^2=1-9=-8$
$(g circ f)(2)=g(5)=3$
#### (b)
$(f circ f)(1)=f(2)=5$
#### (c)
$(f circ g)(5)=f(3)=10$
#### (d)
$(f circ g)(0)$ is undefined because there is no $g(0)$.
#### (e)
$(f circ f^{-1})(2)=2$
#### (f)
$$
(g^{-1} circ f)(1)=g^{-1}(2)=4
$$
$f(g(2))=f(5)=5$
#### (b)
$g(f(4))=g(3)=5$
#### (c)
$(g circ g)(-2)=g(1)=4$
#### (d)
$(f circ f)(2)=f(-1)$
$f(-1)$ does not exist, so $(f circ f)(2)$ is undefined.
$d(5)=80(5)=400$
$C(d(5))=C(400)=0.09(400)=36$
$textbf{It costs $ $36$ to travel for $5$ hours.}$
#### (b)
$C(d(t))$ represents the relationship between the time driven and the cost of gasoline.
$f(g(x))=f(x-1)=3(x-1)^2=3(x^2-2x+1)=3x^2-6x+3$
The domain is $left{xinBbb{R} right}$.
The domain is $left{xinBbb{R} right}$.
$f(g(x))=f(x^2+1)=2(x^2+1)^2+(x^2+1)=2(x^4+2x^2+1)+x^2+1$
$=2x^4+4x^2+2+x^2+1=2x^4+5x^2+3$
The domain is $left{xinBbb{R} right}$
The domain is $left{ xinBbb{R}right}$.
$f(g(x))=f(2x-1)=2(2x-1)^3-3(2x-1)^2+(2x-1)-1$
$=2(8x^3-12x^2+6x-1)-3(4x^2-4x+1)+2x-1-1$
$=16x^3-24x^2+12x-2-12x^2+12x-3+2x-2$
$=16x^3-36x^2+26x-7$
The domain is $left{ xinBbb{R}right}$.
$=2(2x^3-3x^2+x-1)-1$
$=4x^3-6x^2+2x-2-1$
$=4x^3-6x^2+2x-3$
The domain is $left{xinBbb{R}right}$.
$f(g(x))=f(x+1)=(x+1)^4-(x+1)^2=(x+1)^2((x+1)^2-1)$
$=(x^2+2x+1)(x^2+2x+1-1)=(x^2+2x+1)(x^2+2x)$
$=x^4+2x^3+2x^3+4x^2+x^2+2x$
$=x^4+4x^3+5x^2+2x$
The domain is $left{xinBbb{R} right}$
The domain is $left{xinBbb{R} right}$.
$f(f(x))=f()4x=sin 4x$
The domain is $left{xinBbb{R} right}$.
The domain is $left{xinBbb{R} right}$.
$f(g(x))=f(x+5)=|x+5|-2$
The domain is $left{xinBbb{R} right}$.
The domain is $left{xinBbb{R} right}$.
$f circ g=f(sqrt{x-4})=3sqrt{x-4}$
The domain is $left{xinBbb{R}|xgeq4 right}$ and the range is $left{ yinBbb{R}|ygeq0right}$.
$g circ f=g(3x)=sqrt{3x-4}$
The domain is $left{xinBbb{R}|xgeqdfrac{4}{3} right}$ and the range is $left{yinBbb{R}|ygeq 0 right}$.
#### (b)
$f circ g=f(3x+1)=sqrt{3x+1}$
The domain is $left{xinBbb{R}|xgeq -dfrac{1}{3} right}$ and the range is $left{yinBbb{R}|ygeq 0right}$.
$g circ f =g(sqrt{x})=3sqrt{x}+1$
The domain is $left{xinBbb{R}|xgeq 0 right}$ and the range is $left{yinBbb{R}|ygeq 1 right}$.
#### (c)
$f circ g=f(x^2)=sqrt{4-(x^2)^2}=sqrt{4-x^4}$
The domain is $left{xinBbb{R}|-sqrt{2}leq xleqsqrt{2} right}$ and the range is $left{yinBbb{R}|ygeq 0 right}$.
$g circ f=g(sqrt{4-x^2})=(sqrt{4-x^2})^2=4-x^2$
The domain is $left{xinBbb{R}|-2leq x leq2 right}$ and range is
$left{yinBbb{R}| 0 < y <2 right}$.
$f circ g=f(sqrt{x-1})=2sqrt{x-1}$
The domain is $left{x inBbb{R}| x geq 1 right}$ and the range is $left{yinBbb{R}|ygeq1 right}$.
$g circ f=g(2^x)=sqrt{2x-1}$
The domain is $left{xinBbb{R}|xgeq 0 right}$ and the range is $left{ yinBbb{R}| ygeq 0right}$.
#### (e)
$f circ g=f(log x)=10^{log x}=x$
The domain is $left{xinBbb{R} right}$ and the range is $left{yinBbb{R} right}$
#### (f)
$f circ g =f(5^{2x}+1)=sin(5^{2x}+1)$
The domain is $left{xinBbb{R} right}$ and the range is $left{ yinBbb{R}| -1 leq y leq 1right}$.
$g circ f=g(sin x)=5^{2sin x}+1$
The domain is $left{xinBbb{R} right}$ and the range is $left{yinBbb{R}|dfrac{26}{25}leq y leq 26 right}$.
Answers may vary. For example, $f(x)=sqrt{x}$ and $g(x)=x^2+6$
#### (b)
Answers may vary. For example, $f(x)=x^6$ and $g(x)=5x-8$
#### (c)
Answers may vary. For example, $f(x)=2^x$ and $g(x)=6x+7$
#### (d)
Answers may vary. For example,$f(x)=dfrac{1}{x}$ and $g(x)=x^3-7x+2$
#### (e)
Answers may vary. For example, $f(x)=sin^2 x$ and $g(x)=10x+5$
#### (f)
Answers may vary. For example, $f(x)=sqrt[3]{x}$ and $g(x)=(x+4)^2$
$(fcirc g)(x)=f(x^2)=2x^2-1$
It is compressed by a factor of $2$ and translated down $1$ unit.
$f(g(x))=f(3x+2)=2(3x+2)-1=6x+4-1=6x+3$
The slope of $g(x)$ has been multiplied by $2$, and the $y$-intercept of $g(x)$ has been vertically translated $1$ unit up.
#### (b)
$$
g(f(x)=g(2x-1)=3(2x-1)+2=6x-3+2=6x-1
$$
The slope of $f(x)$ has been multiplied by $3$.
f(g(x))=f(0.75x)=0.08(0.75x)=0.06x
$$
$d(s)=sqrt{16+s^2}; s(t)=560t$
#### (b)
$d(s(t))=sqrt{16+313600t^2}$, where $t$ is the time in hours and $d(s(t)$ is the distance in kilometers.
$textbf{The car is running most economically $2$ hours into the trip}$.
Graph $B(b)$; $f(x)$ is translated $3$ units to the right.
Graph $C(d)$; $f(x)$ is horizontally compressed by a factor of $dfrac{1}{2}$.
Graph $D(1)$; $f(x)$ is translated $4$ units down.
Graph $E(g)$; $f(x)$ is translated $3$ units up.
Graph $F(c)$; $f(x)$ is reflected in the $y$-axis.
$f(x)=dfrac{4}{x-3}$; $g(x)=1$
$textbf{Product:}$ $y=ftimes g$
$f(x)=x-3$;
$g(x)=dfrac{x+1}{(x-3)^2}$
$textbf{Quotient:}$ $y=fdiv g$
$f(x)=1+x; g(x)=x-3$
$textbf{Composition:}$ $y=f circ g$
$f(x)=dfrac{4}{x}+1$; $g(x)=x-3$
$f(k)=f(x(t(k)))$
$=f(x(3k-2))$
$=f(3(3k-2)+2)$
$=f(9k-6+2)$
$=f(9k-4)$
$=3(9k-4)-2$
$=27k-12-2$
$=27k-14$
#### (b)
$f(k)=f(x(t(k)))$
$=f(x(3k-5))$
$=fleft(sqrt{3(3k-5)-1} right)$
$=fleft(sqrt{9k-15-1} right)$
$=fleft(sqrt{9k-16} right)$
$$
=2sqrt{9k-16}-5
$$