Question

Find the sum of the first 20terms of the A.P. logx,logx^2,logx^3,logx^4

Answer 1

note that the sequence is

1logx + 2logx + 3logx + ... = logx(1+2+...+20)
So S20 = logx * 20*21/2 = 210 logx (for x > 0 ... why?)