Find the coefficient of `x^k in1+(1+x)+(1+x)^2++(1+x)^n(0lt=klt=n)dot`

Find the coefficient of x^n in the expansion of (1+x)(1+x)^ndot

Find the coefficient of x^(20) in (x^2+2+1/(x^2))^(-5)(1+x^2)^(40)dot

Find the coefficient of x^n in the expansion of (1-9x+20 x^2)^(-1)dot

Find the coefficient of x^r in the expansion of 1 +(1 + x) + (1 + x)^2 +.......+ (1 + x)^n .

If n is a positive integer, find the coefficient of x^(-1) in the expansion of (1+x)^n(1+1/x)^ndot

The coefficient of x^(n) in (x+1)/((x-1)^(2)(x-2)) is

Find the coefficient of x^5 in the expansion of (1+x)^(21)+(1+x)^(22)+.........+(1+x)^(30)dot

The coefficient of x^n in the expansion of (1+x)(1-x)^n is

Find the coefficient of x^n in (1+x/(1!)+(x^2)/(2!)+........+(x^n)/(n !))^2 .

If A and B are the coefficients of x^n in the expansion (1 + x)^(2n) and (1 + x)^(2n-1) respectively, then