If the coefficients of rth and (r + 1)th terms in the expansion of (3+7x)29 are equal, then r equals

We have Tr+1=29Cr329−r(7x)r= 29Cr×329−r×7rxrCoefficient of (r+1)th term is  29Cr×329−r×7rand coefficient of rth term is  29Cr−1×330−r×7r−1From given condition, 29Cr×329−r×7r=29Cr−1×330−r×7r−1⇒ 29Cr 29Cr−1=37                nCr nCr−1=n-r+1r⇒30−rr=37 or r=21