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1/52+49/52×51+49×48/52×51×50+.+49×...×1/52×...×3=?
1/52+49/52×51+49×48/52×51×50+.+49×...×1/52×...×=?
1/52+49/52×51+49×48/52×51×50+......+49×...×1/52×...×3=?
人气:467 ℃ 时间:2019-11-04 14:31:30
解答
原式=51×50/52×51×50+50×49/52×51×50+49×48/52×51×50+48×47/52×51×50+.2×1/52×51×50=﹙51×50+50×49+49×48+48×47+.+2×1﹚/52×51×50因为 1×2=1×2×3×1/3 2×3=1/3×﹙2×3×4-1×2×...
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