递等式计算:1/13×15+1/15×17+1/17×19+……+1/37×39

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递等式计算:1/13×15+1/15×17+1/17×19+……+1/37×39递等式计算:1/13×15+1/15×17+1/17×19+……+1/37×39递等式计算:1/13×15+1/15×1

递等式计算:1/13×15+1/15×17+1/17×19+……+1/37×39
递等式计算:1/13×15+1/15×17+1/17×19+……+1/37×39

递等式计算:1/13×15+1/15×17+1/17×19+……+1/37×39
=1/2×(1/13-1/15+1/15-1/17+……+1/37-1/39)
=1/2×(1/13-1/39)
=1/39

1/13×15+1/15×17+1/17×19+……+1/37×39
=(1/13-1/15+1/15-1/17+1/17-1/19+……+1/37-1/39)÷2
=(1/13-1/39)÷2
=2/39÷2
=1/39

1/2(1/13-1/15+1/15-1/17……1/37-1/39)
=1/2(1/13-1/39)
=1/39

=1/2(1/13-1/15)+1/2(1/15-1/17)+......+1/2(1/37-1/39)
=1/2(1/13-1/15+1/15-1/17+......+1/37-1/39)
=1/2(1/13-1/39)
=1/39