Question

If f(x) = 8 – 10x and g(x) = 5x + 4, what is the value of (fg)(–2)?

Answer 1

F(x) = 8 - 10x

g(x) = 5x + 4

Finding (fg)(-2).

First let us find fg(x),  this is the same as f(g(x))

f(g(x))

f(5x + 4)

Recall, f(x) = 8 - 10x, therefore f(5x + 4) would be such that anywhere we see x in the f(x), we replace it with 5x + 4

f(x) = 8 - 10x

f(5x +4) =  8 - 10(5x + 4)

             =  8 - 50x - 40

             = -50x + 8 - 40

             =  -50x - 32

f(g(x)) = fg(x) = -50x - 32

fg(-2) = -50*(-2) - 32 = 100 - 32 = 68

Therefore fg(-2) = 68

I hope this helped.