x=(5^(2))/((-2)^(0) (-4)^(2)) y=(-1-(1)/(8^(7)))^(-4) R=((x)/(4) (x^(3))/(2) (x^((2)/(3)))/(3) (6)/((xy)^(6)))^((1)/(3)) f=2x 2y \sum_(i=250)^(500) (i)/(3R \sqrt(x) y^(2))