等差数列中,a1=3,a100=36,则a3+a98=

问题描述:

等差数列中,a1=3,a100=36,则a3+a98=

a3=a1+2d (d为公差)
a100=a98+2d(即:a98=a100-2d)
∴a3+a98=a1+2d +a100-2d
=a1+a100
=39