3*4+2*4的平方+2*4的3次方+·····2*4的n次方-（2n+1)*4的n+1次=-3s 求s是什么
网友回答
3*4+2*4^2+2*4^3+...+2*4^n-(2n+1)*4^(n+1)
=4+2*(4+4^2+...+4^n)-(2n+1)*4^(n+1)
=4+2*(4^(n+1)-4)/3-(2n+1)*4^(n+1)
=[(2*4^(n+1)+4]/3-(2n+1)*4^(n+1)
=-[(6n+1)*4^(n+1)-4)/3
s=[(6n+1)*4^(n+1)-4)/9