(99²+98²+…+90²)-(89²+88²+…+80²)

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(99²+98²+…+90²)-(89²+88²+…+80²)
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(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