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by jxyzs @ 2019-09-26 20:57:38
令左边等于s,用2s减s就好
by jxyzs @ 2019-09-26 20:58:17
猫猫！
by Winterain @ 2019-09-26 20:58:20
@[Null_Cat](/space/show?uid=213346)
by jxyzs @ 2019-09-26 20:58:21
最直接的方法先加上一再减一
by my_load @ 2019-09-26 20:58:25
2^0+2^0=2^1;
2^1+2^1=2^2……
2^0+2^1+2^2+……+2^(n-1)
=2^0+2^0+2^1+2^2+……+2^(n-1)-2^0
=2^n-1
by A_Đark_Horcrux @ 2019-09-26 20:58:53
左式$\times 2$ 再减左式
这是钓鱼帖吧
by installb @ 2019-09-26 20:58:54
神猫qwq
by 紫陰花 @ 2019-09-26 20:59:00
@[installb](/space/show?uid=31440) 不钓鱼qwq窝真的不会证明qaq
by Null_Cat @ 2019-09-26 20:59:24
@[jxyzs](/space/show?uid=133922) $\mathfrak{Danke!}$
by Null_Cat @ 2019-09-26 21:00:06