Question

奥数题1×99+2×97+3×95+……+50×1=?

Answer 1

规律为An=n[100-(2n-1)]=100n-2n^2+n=101n-2n^2

1×99+2×97+3×95+……+50×1=101(1+2+3……+50)-2(1^2+2^2+3^2+……+50^2)=