Question

已知(1 + x ) + (1 + x )2 + … + (1 + x )n = a0 + a1x + a2x2 + …

Answer 1

令x=1

则1+x=2

所以左边是2+……+2^n=2^(n+1)-2

右边=a0+a1+……+a(n-1)+an=n+(29-n)+1=30

即2^(n+1)-2=30

2^(n+1)=32=2^5

n+1=5

n=4