Question

If f(x)= x^2 + 5 and g(x) =5x+4, what is[f o g(6)

Answer 1

You can do this a couple ways: either find g(6), then find f(x) of whatever that gives you (a 2-step process), or come up with a new expression to represent f(g(x)) and sub 6 into that (a 1-step process). I like the 1-step process more.

g(x) = 5x + 4; We want to sub this expression into every x in f(x) to get f(g(x)). If f(x) = x^2 + 5, then f(g(x)) = g(x)^2 + 5 = (5x + 4)^2 + 5. Now you can sub 6 into this equation and solve: f(g(6)) = (5(6) + 4)^2 + 5 = 1161.