Value of r for which ^ 15 C_ r + 3 = ,^ 15 C_ 2r - 6 is - Vidyadip

MCQ

Value of $r$ for which $^{15}{C_{r + 3}} = {\,^{15}}{C_{2r - 6}}$ is

A
$2$
B
$4$
✓
$6$
D
$-9$

✓

Answer

Correct option: C.

$6$

c
(c) Either $r + 3 = 2r - 6$
or $r + 3 + 2r - 6 = 15,\,\,({\,^n}{C_r} = {\,^n}{C_{n - r}})$
==> $r = 9$ or $r = 6$.

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