Question

已知等差数列中,a6=5,a3+a8=5,求首项a1和公差d.

Answer 1

a1+5*q=5 a1=5-5q

a1+2q+a1+7q=5 2a1+9q=5

2(5-5q)+9q=5

10-10q+9q=5

q=5

a1=-20