1.∑r=0n(nr)2\displaystyle\sum_{r=0}^{n} \binom{n}{r}^{2}r=0∑n(rn)2 is equal toa.(2nn)\binom{2n}{n}(n2n)b.(2n−1n−1)\binom{2n-1}{n-1}(n−12n−1)c.22n−1(2nn)2^{2n-1}\binom{2n}{n}22n−1(n2n)d.2n−1(2n−1n)2^{n-1}\binom{2n-1}{n}2n−1(n2n−1)Login to continueOnly logged in users canattempt or see the solution.
