100X100-99X99-98X98-97X97+…+2X2-1X1=?

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100X100-99X99-98X98-97X97+…+2X2-1X1=?
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100X100-99X99-98X98-97X97+…+2X2-1X1=?
100X100-99X99-98X98-97X97+…+2X2-1X1=?

100X100-99X99-98X98-97X97+…+2X2-1X1=?
你应该是写错一个符号,就是99X99-98X98应该是+
100x100-99x99+98x98-97x97+.+4x4-x4-3x3+2x2-1
=(100+99)(100-99)+(98+97)(98-97)+.+(4+3)(4-3)+(2+1)(2-1)
=199+195+.7+3
=(199+3)+(195+7)+(191+11)+(187+15)+.+(103+99)
=5050