等差数列an中公差为1/2,且a1十a3十a5.十a99=60则a2十a4十a6十.十a100=
问题描述:
等差数列an中公差为1/2,且a1十a3十a5.十a99=60则a2十a4十a6十.十a100=
答
a2=a1+d
a4=a3+d
a6=a5+d
.
a100=a99+d
所以
a2十a4十a6十.十a100=60+49*1/2=84.5