Vikas TU9 Years agoFirstly,muktiply all the 4 terms as usual.and get the r terms in the power of 4, 3 ,2 and 1.And hence apply the summation formulae for that simply:For summation of r from n=1 to n is => n(n+1)/2for r^2 the summation is: => n(n+1)(2n+1)/6for r^3 it is: n^2(n+1)^2/4 and like this.