If the coefficient of (3r+4)th term and (2r – 2)th term in the expansion of (1 + x)20 are equal then r is equal to :

If the coefficient of $(3 r + 4) t h$ term and $(2 r - 2) t h$ term in the expansion of ${(1 + x)}^{20}$ are equal then $r$ is equal to :

$^{20} C_{3 r + 3} =^{20} C_{2 r - 3} \Rightarrow (3 r + 3) + (2 r - 3) = 20 \Rightarrow r = 4$

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