(p + 2)th term from the end in the binomial expansion of
x2−2x22n+1 is
2n+1C2n−n(−2)2n−px2p+1−2n
2n+1C2n−n(−2)2n−px2n−2p
2n+1C2n−p(−2)2n−px2n−2p+1
2n+1C2n−p(−2)2n−px2p−1+2n
(p + 2)th term from the end
=[2n+2−(p+1)]th=(2n−p+1)th
from the beginning
and T2n−p+1=2n+1C2n−px22n+1−(2n−p)−2x22n−p
=2n+1C2n−p(−2)2n−px2p+1−2n