2/3x5+2/5x7+…+2/31x33
=(5-3)/3*5+(7-5)/5x7+…+(33-31)/31x33
=(5/3*5-3/3*5)+(7/5x7-5/5x7)+…+(33/31x33-31/31x33)
=(1/3-1/5)+(1/5-1/7)+…+(1/31-1/33)
=1/3-1/5+1/5-1/7+…+1/31-1/33
=1/3+(-1/5+1/5)+(-1/7+1/7)+…+(-1/31+1/31)-1/33
=1/3-1/33
=10/33
2/3x5+2/5x7+…+2/31x33
2个回答
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