1 y 1 2x 1 2 5y 4 5x 1 July 8, 2019 16 32 64 128 (5y ^ 2)/(1 - y ^ 2) / (1 - 1/(1 - y)) 2) (5y ^ 2)/(1 - y ^ 2) / (1 - 1/(1 - y))
