rth term in the expansion of (a+2x)n is
n(n+1).....(n−r+1)r!an−r+1(2x)r
n(n−1).....(n−r+2)(r−1)!an−r+1(2x)r−1
n(n+1).....(n−r)(r+1)!an−r(x)r
None of these
rth term of (a+2x)n is nCr−1(a)n−r+1(2x)r−1
= n!(n−r+1)!(r−1)!an−r+1(2x)r−1
= n(n−1).....(n−r+2)(r−1)!an−r+1(2x)r−1