1/3*4+1/4*5+1/5*6+······+1/19*20簡便方法計算

1/3*4+1/4*5+1/5*6+······+1/19*20簡便方法計算

1/3*4+1/4*5+1/5*6+······+1/19*20
=1/3-1/4+1/4-1/5+1/5-1/6+…+1/19-1/20
=1/3-1/20
=17/60

Elden Ring Premiere

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