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If the coefficients of (2r + 4)th term a...

If the coefficients of `(2r + 4)th` term and ` (r - 2)th` term in the expansion of `(1 + x)^(18)` are equal,find `r`.

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Given
`(1+x)^{18}`
the coefficient of the rth term in the expansion of `(1+x)^{n}` is `\ ^{n} C_{r-1}`
the coefficients of the `(2 r+4)` th and `(r-2)` th terms are `\ ^{18} C_{2 r+4-1}` and `\ ^{18} C_{r-2-1}`
For these coefficients to be equal, we must have
...
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