Question

Which two functions are inverses of each other?
f(x) = x, g(x) = –x
f(x) = 2x, g(x) =-(1/2)x
f(x) = 4x, g(x) = (1/4)x
f(x) = –8x, g(x) = 8x

Answer 1

f(x) and g(x) are inverses iff
f(g(x))=x and g(f(x))=x

Answer 2

so for example
if f(x)= x and g(x)=-x
then f(g(x))=f(-x)=-x but this is not x
so the first one is not a pair of inverse functions
you try the others