1/2*4*6=(1/4)*(1/2*4-1/4*6)1/4*6*8=(1/4)*(1/4*6-1/6*8)……所以原式=(1/4)*(1/2*4-1/4*6+1/4*6-1/6*8+……+1/10*12-1/12*14)=(1/4)*(1/2*4-1/12*14)=5/168
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