Question

f(x)=3x+5 and g(x)=-4x+7 find (fog)(-4)

Answer 1

Given: f(x)=3x+5 and g(x)=-4x+7
Now in order to find fog(-4) first we shall find fog(x)
to do this we shall substitute x= g(x)=-4x+7 in f(x)
f(x)=3x+5
i.e. f(g(x))=3(-4x+7)+5 = -12x +21 +5 = -12x+26
hence f(g(x))= -12x+26
Now we substitute x=-4, we find:
f(g(-4))= -12(-4)+26 = 48 +26 = 74
f(g(-4)) = 74
or fog(-4) =74

@iedoubina