数列{an}的首项为3,{bn}为等差数列且bn=an+1-an(n∈N+),若b3=-2,b10=12,则a8=（A）0（B）3(C)数列{An}的首项为3，{Bn}为等差数列且Bn=A(n+1)-An(n∈N+),若B3=-2,B(10)=12,则A8等于多少

Question

数列{an} 的首项为3,{b n}为等差数列且b n =an+1- an (n∈N+),若b3=-2, b10 =12,则a8= （A）0 （B）3 (C)
数列{An} 的首项为3，{B n}为等差数列且B n =A(n+1)- An (n∈N+),若B3=-2, B(10) =12,则A8等于多少

Answer 1

bn=b1+d,b10=b3+7d,即12=-2+7d,得d=2,b3=b1+2d,则b1=b3-2d=-2-2*2=-6,故bn=b1+（n-1）d=-6+2（n-1）=2n-8.b1=a2-a1b2=a3-a2……bn-1=an-an-1bn=an+1-anb1+b2+b3+……+bn-1+bn=an+1-a1b1+b2+b3+……+bn= -6*n+2*n(n-1...