First slide

Combinations

Question

$^{n} C_{r} + 2^{n} C_{r - 1} +^{n} C_{r - 2}$ is equal to

Moderate

A

$^{n + 1} C_{r}$
B

$^{n} C_{r - 1}$
C

$n - 1_{C_{r - 1}}$
D

$^{n + 2} C_{r}$

Solution

We have
$\begin{array}{l} ^{n} C_{r} + 2^{n} C_{r - 1} +^{n} C_{r - 2} \\ = (^{n} C_{r} +^{n} C_{r} + 1) + (^{n} C_{r - j} +^{n} C_{r - 2}) \\ =^{n + 1} C_{r} +^{n + 1} C_{r} - 1 =^{n + 2} C_{γ} \end{array}$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App