Find a if the `17^th` and `18^th` terms of the expansin `(2 + a)^50`are equal.

If the coefficients of (r-5)^th and (2r - 1)^th terms in the expansion of (1 + x)^34 are equal, find r.

r and n are positive integers r gt 1 , n gt 2 and coefficient of (r + 2)^(th) term and 3r^(th) term in the expansion of (1 + x)^(2n) are equal, then n equals

Find the 4^th term in the expansion of (x-2y)^12 .

If the coefficients of the r^(th) term and the (r + 1)^(th) term in the expansion of (1 + x)^(20) are in the ratio 1:2 , then r is equal to

Find the 10^(th) and n^(th) terms of the G.P . 5, 25,125 ...............