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1-1/5-1/45-1/117-1/221-1/375
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1-1/5-1/45-1/117-1/221-1/375
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1-1/5-1/45-1/117-1/221-1/357
=1-1/(1x5)-1/(5x9)-1/(9x13)-1/(13x17)-1/(17x21)
=1-[1/(1x5)+1/(5x9)+1/(9x13)+1/(13x17)+1/(17x21)]
=1-[1/4(1-1/5)+1/4(1/5-1/9)+1/4(1/9-1/13)+1/4(1/13-1/17)+1/4(1/17-1/21)]
=1-1/4(1-1/5+1/5-1/9+1/9-1/13+1/13-1/17+1/17-1/21)
=1-1/4(1-1/21)
=1-1/4x20/21
=1-5/21
=16/21
=1-1/(1x5)-1/(5x9)-1/(9x13)-1/(13x17)-1/(17x21)
=1-[1/(1x5)+1/(5x9)+1/(9x13)+1/(13x17)+1/(17x21)]
=1-[1/4(1-1/5)+1/4(1/5-1/9)+1/4(1/9-1/13)+1/4(1/13-1/17)+1/4(1/17-1/21)]
=1-1/4(1-1/5+1/5-1/9+1/9-1/13+1/13-1/17+1/17-1/21)
=1-1/4(1-1/21)
=1-1/4x20/21
=1-5/21
=16/21
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