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Given the definitions of 
f(x) and 
g(x) below, find the value of 
(g@f)(-7).

{:[f(x)=2x+15],[g(x)=2x^(2)+5x+4]:}
Answer:

Given the definitions of f(x) f(x) and g(x) g(x) below, find the value of (gf)(7) (g \circ f)(-7) .\newlinef(x)=2x+15g(x)=2x2+5x+4 \begin{array}{l} f(x)=2 x+15 \\ g(x)=2 x^{2}+5 x+4 \end{array} \newlineAnswer:

Full solution

Q. Given the definitions of f(x) f(x) and g(x) g(x) below, find the value of (gf)(7) (g \circ f)(-7) .\newlinef(x)=2x+15g(x)=2x2+5x+4 \begin{array}{l} f(x)=2 x+15 \\ g(x)=2 x^{2}+5 x+4 \end{array} \newlineAnswer:
  1. Understand Notation: First, we need to understand the notation (g@f)(x)(g@f)(x). This notation means that we first apply the function ff to xx, and then apply the function gg to the result of f(x)f(x). This is also known as the composition of functions, denoted by (gf)(x)(g \circ f)(x).
  2. Find f(7)f(-7): Now, let's find f(7)f(-7) using the definition of f(x)=2x+15f(x) = 2x + 15.f(7)=2(7)+15=14+15=1f(-7) = 2(-7) + 15 = -14 + 15 = 1.
  3. Find g(f(7))g(f(-7)): Next, we will use the result of f(7)f(-7) to find g(f(7))g(f(-7)) by substituting 11 into g(x)g(x), where g(x)=2x2+5x+4g(x) = 2x^2 + 5x + 4.g(1)=2(1)2+5(1)+4=2+5+4=11g(1) = 2(1)^2 + 5(1) + 4 = 2 + 5 + 4 = 11.
  4. Conclude Result: Since we have found g(1)g(1), and we know that f(7)=1f(-7) = 1, we can conclude that (g@f)(7)(g@f)(-7) is equal to g(f(7))g(f(-7)) which is g(1)g(1). Therefore, (g@f)(7)=11(g@f)(-7) = 11.

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