沒有就map一個出來吧 XD
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1/2x +1/2(1/2x + 1/2(1/2x + 1/2(1/2x + ... = y
1/2(1/2x + 1/2(1/2x + 1/2(1/2x + ... = y - 1/2x
1/2x + 1/2(1/2x + 1/2(1/2x + ... = 2y - 1/x = y
y=1/x
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1/2x +1/2(1/2x + 1/2(1/2x + 1/2(1/2x + ... = y
1/2(1/2x + 1/2(1/2x + 1/2(1/2x + ... = y - 1/2x
1/2x + 1/2(1/2x + 1/2(1/2x + ... = 2y - 1/x = y
y=1/x