1/2X(2+2)+1/3X(3+2)+1/4X(4+2)+……+1/8(8+2)+1/9(9+2)
=8+2(1/2+1/3+1/4+1/5+1/6+1/7+1/8+1/9)
=8+2(1/2+1/3+1/6+1/4+1/8+1/5+1/7+1/9)
=8+2(1+3/8+1/5+1/7+1/9)
=10+2(3/8+1/5+1/7+1/9)到这就要自己算数啦
=10+2*(2089/2520)
=10+2089/1260
=14689/1260,
1/2×4+1/3×5+1/4×6+1/5×7+……+1/8×10+1/9×11
5个回答
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