If the coefficient of the 4^{th} term in the | vedclass

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(C) The general term in the expansion of $(a + b)^n$ is given by $T_{r+1} = {}^nC_r a^{n-r} b^r$.For the $4^{th}$ term,$r = 3$,so $T_4 = {}^nC_3 a^{n-

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$8$

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(C) The general term in the expansion of $(a + b)^n$ is given by $T_{r+1} = {}^nC_r a^{n-r} b^r$.For the $4^{th}$ term,$r = 3$,so $T_4 = {}^nC_3 a^{n-3} b^3$.The coefficient of the $4^{th}$ term is ${}^nC_3 = 56$.Using the formula ${}^nC_3 = \frac{n(n-1)(n-2)}{3 	imes 2 	imes 1} = 56$.$n(n-1)(n-2) = 56 	imes 6$.$n(n-1)(n-2) = 336$.We look for three consecutive integers whose product is $336$.$8 	imes 7 	imes 6 = 336$.Therefore,$n = 8$.

If the coefficient of the $4^{th}$ term in the expansion of $(a + b)^n$ is $56$,then $n$ is

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