Question

数列an的首项为3 bn为等差数列 且bn=an+1-an 若b3=-2 b10=12 则a8=

Answer 1

3=-2,b10=12

7d=b10-b3=14

d=2

bn=-2+2(n-3)=2n-8

a8

=(a8-a7)+(a7-a6)+.+(a2-a1)+a1

=b7+b6+.+b1+3

=[6+4+2+0+(-2)+(-4)+(-6)]+3

=3