If coefficient of {(2r + 4)^{th}} and {(r - 2)^{th}} terms in expansion of {(1 + x)^{18}} are equal,

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7.Binomial Theorem

easy

If the coefficient of ${(2r + 4)^{th}}$ and ${(r - 2)^{th}}$ terms in the expansion of ${(1 + x)^{18}}$ are equal, then$ r=$

A

$12$

B

$10$

C

$8$

D

$6$

Solution

(d) $^{18}{C_{2r + 3}}{ = ^{18}}{C_{r – 3}}\,\,\, \Rightarrow 2r + 3 + r – 3 = 18 \Rightarrow r = 6$

Standard 11

Mathematics

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