Question

Find (fg)(-4) when f(x) = x + 5 and g(x) = 5x2 + 10x - 5.

Answer 1

f(x) = x+5

f(-4) = -4+5

f(-4) = 1

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g(x) = 5x^2+10x-5

g(-4) = 5(-4)^2+10(-4)-5

g(-4) = 5(16)+10(-4)-5

g(-4) = 80-40-5

g(-4) = 35

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(fg)(x) = f(x)*g(x)


(fg)(-4) = f(-4)*g(-4)


(fg)(-4) = 1*35


(fg)(-4) = 35

Answer 2

fg=(x+5)(5x2 +10x -5)
fg=(5x3 +10x2 -5x +25x2 +50x -25)
fg=5x3 + 35x2 + 40x -25

fg(-4) = 5(-4)^3 +35(-4)^2 +50(-4) -25
fg(-4) = 64(5) + 35(16) + 50(-4) -25