Q. If $^{n^{2} - n} C_{2} =^{n^{2} - n} C_{10},$ then $n =$

2030 260 Binomial Theorem Report Error

A

12

B

4 only

C

-3 only

D

4 or -3

Solution:

$^{n^{2} - n} C_{2} =^{n^{2} - n} C_{10}$
$\Rightarrow^{n^{2} - n} C_{n^{2} - n - 2} =^{n^{2} - n} C_{10}$
$\Rightarrow n^{2} - n - 2 = 10$ or $n = 4, - 3.$