Use f(x) = 1/2x and f -1(x) =2x to solve the problems. f−1(f(x)) = f(f−1(x))

Can some one me with these questions

If the ratio of sum of the first m and n terms of an ap is m2 : n2 , show that the ratio of its mth and nth terms is (2m − 1) : (2n − 1).

How do i solve uniform motion problems?