已知等差数列an的公差d大于0,且a3,a5是方程x^2-14x+45=0的两根
求数列an的通项公式
记bn=2的an次方+你,求数列bn的前n项和Sn
an =a1+(n-1)da3+a5= 14 2a1+6d=14a1+3d=7 (1)a3.a5=45(a1+2d)(a1+4d)=45(7-d)(7+d)=45d^2=4d=2from (1),a1=1an = 1+2(n-1) = 2n-1bn=2^(an) +n= 2^(2n-1) +nSn = b1+b2+...+bn= 2( 2^(2n) -1) /(4-1) + n(n+1)/2=(2...
