If-the-coefficient-of-2r-4-th-and-r-2-th-terms-in-the-expansion-of-1-x-18-are-equal-then-the-value-of-r-is-

Question Number 63940 by gunawan last updated on 11/Jul/19

If the coefficient of (2 r + 4) th and (r - 2) th

terms in the expansion of {(1 + x)}^{18} are

equal, then the value of r is

Answered by mr W last updated on 11/Jul/19

c o e f . o f k + 1 t h t e r m i s

C_{k}^{18} = C_{18 - k}^{18}

(2 r + 4 - 1) + (r - 2 - 1) = 18

\Rightarrow r = 6

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