a) f(x) = x - 4 , g(x) = x + 4
⇒ f( g(x) ) = x + 4 - 4 = x
g( f(x) ) = x - 4 + 4 = x
⇒ f and g are not inverses of each other
b) f(x) = -1/(3x) , x ≠ 0 ; g(x) = 1/(3x) , x ≠ 0
⇒ f( g(x) ) = -1/( 3*(1/(3x)) ) = -1/(1/x) = -x
g (f(x) ) = 1/( 3*(-1/(3x)) ) = 1/( -1/x) = -x
⇒ f and g are not inverses of each other