19 is easy:
f(x) = 9/x + 2
g(x)= x^2
f(g(x)) = f(x^2) = 9/x^2 + 2
so y = f(g(x)) = 9/x^2 + 2
20. f(x)=9x+3
g(x)=(x-3)/9
f(g(x))=f((x-3)/9=9((x-3)/9)+3
=(x-3)+3
=x
g(f(x))=g(9x+3)=((9x+3)-3)/9
=9x/9
19. ans is f(x) = 9/x + 2 and g(x)= x^2
y=f(g(x))=f(x^2)=9/x^2 + 2
20. alternate proof:
f(x)=9x+3
so y=9x+3
9x=y-3
x=(y-3)/9
swapping x <=> y
y=(x-3)/9=g(x)
so f and g are inverses
