(99²+98²+…+90²)-(89²+88²+…+80²)

来源:学生作业帮助网 编辑:作业帮 时间:2024/07/21 10:09:20
(99²+98²+…+90²)-(89²+88²+…+80²)
xP] ڈq=$]x~ӐKgvó#vޠpI@%#lJ4x[gѫҊTFCh =j.|-l"Hʵ;äPpfl \]< /ۧq]Q= _u9"[#Ihퟋ

(99²+98²+…+90²)-(89²+88²+…+80²)
(99²+98²+…+90²)-(89²+88²+…+80²)

(99²+98²+…+90²)-(89²+88²+…+80²)
=(99²-89²)+(98²-88²)+……+(90²-80²)
=(99+89)(99-89)+(98+88)(98-88)+……+(90+80)(90-80)
=(99+89)*10+(98+88)*10+……+(90+80)*10
=(80+81+82+……+99)*10
=(80+99)*20/2*10
=17900

=(99^2-89^2)+(98^2-88^2)+....+(90^2-80^2)
=10*[188+186+....+170]
=10*1790
=17900