How do you find [f • g](x) and [g • f](x) if $F(x) = x^2 + 2x$ and $G(x) = x-9$ ?

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Answer 1 · 2015-09-29T06:01:36

$(f•g)(x)=x^2-16x+63$
$(g•f)(x)=x^2+2x-9$

$(f•g)(x)=f(g(x))=f(x-9)=(x-9)^2+2(x-9)$
$(f•g)(x)=x^2-18x+81+2x-18=x^2-16x+63$

$(g•f)(x)=g(f(x))=g(x^2+2x)=x^2+2x-9$

How do you find [f • g](x) and [g • f](x) if F(x) = x^2 + 2xF(x) = x^2 + 2x and G(x) = x-9G(x) = x-9?