If sum of the coefficients in the expansion of x+1xnis 128., then coefficient of x in the expansion of x+1xnis

Sum of the coefficients in the expansion of  x+1xnis equal to 2n .∴ 2n=128=27⇒n=7Now, Tr + 1, the (r + 1)th term in the expansion of x+1x7is Tr+1=7Crx7−r1xr=7Crx7−2rFor the coefficient of x, we set  7 – 2r = 1⇒ r = 3.Thus, coefficient of x in the expansion of x+1x7is  7C3=35