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Question

Find (fg)(2)(f \cdot g)(-2) for the following functions.

f(x)=x2+2x2g(x)=2x+3\begin{array}{l}{f(x)=-x^{2}+2 x-2} \\ {g(x)=2 x+3}\end{array}

A. -20 B. 8 C. 120 D. 215

Solution

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Answered 2 years ago
Answered 2 years ago
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By definition: (fg)(x)=f(x)g(x)(f\cdot g)(x)=f(x)\cdot g(x).

First, we find (fg)(x)(f\cdot g)(x).

(fg)(x)=f(x)g(x)=(x2+2x2)(2x+3)=2x33x2+4x2+6x4x6=2x3+x2+2x6\begin{align*} (f\cdot g)(x)&=f(x)\cdot g(x)\\ &=(-x^2+2x-2)\cdot (2x+3)\\ &=-2x^3-3x^2+4x^2+6x-4x-6\\ &=-2x^3+x^2+2x-6 \end{align*}

Next, we replace the variable xx with the value 2-2.

(fg)(2)=2(2)3+(2)2+2(2)6=16+446=10\begin{align*} (f\cdot g)(-2)&=-2\cdot(-2)^3+(-2)^2+2\cdot(-2)-6\\ &=-16+4-4-6\\ &=\boxed{10} \end{align*}

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