If the number of terms in the expansion of1−2x+4x2n,x≠0, is 28, then the sum of the coefficients of all the terms in this expansion, is

The number of terms in the expansion of f=1-2x+4x2n   is (n+2)C2∴ Given (n+2)C2=28⇒(n+2)(n+1)2=28⇒(n+2)(n+1)=56⇒n=6 Sum of the coefficients =f(1)=(1-2+4)n=3n=36=729