1+(1+2)+(1+2+3)+.+(1+2.50)等于几?
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![1+(1+2)+(1+2+3)+.+(1+2.50)等于几?](/uploads/image/z/4004746-34-6.jpg?t=1%2B%281%2B2%29%2B%281%2B2%2B3%29%2B.%2B%281%2B2.50%29%E7%AD%89%E4%BA%8E%E5%87%A0%3F)
1+(1+2)+(1+2+3)+.+(1+2.50)等于几?
1+(1+2)+(1+2+3)+.+(1+2.50)等于几?
1+(1+2)+(1+2+3)+.+(1+2.50)等于几?
1230
=1+1+2+1+2+3+1+2+3+4...........+1+2+3......+50
=50*1+49*2+48*3+47*4.........+1*50 (两个因数和为51)
=2*(50*1+49*2.........+26*25)
剩下自己算