a1+a4+a7+……+a97=50a3+a6+a9+.+a99所求每项都和已知每项差2da3=a1+2da6=a4+2da9=a7+2d...a99=a97+2d∴所求=a1+2d+a4+2d+a7+2d+.a97+2d=(a1+a4+a7+...+a97)+n*2dn是这列数有多少项我们先看a1+a4+a7+.a97角标呈等差...