tính nhanh A=1/3-3/4-(-3/5)+1/72-2/9-1/36+1/15

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1. `A=1/3-3/4-(-3/5)+1/72-2/9-1/36+1/15`

   `A=1/3-3/4+3/5+1/72-2/9-1/36+1/15`

   `A=(1/3+3/5+1/15)-(3/4+2/9+1/36)+1/72`

   `A=1-1+1/72`

   `A=1/72`

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2. `A = 1/3 – 3/4 – (-3)/5 + 1/72 – 2/9 – 1/36 + 1/15`

   `= 1/3 – 3/4 + 3/5 + 1/72 – 2/9 – 1/36 + 1/15`

   `= ( 1/3 + 3/5 + 1/15 ) – ( 3/4 + 2/9 +1/36 ) + 1/72`

   `= ( 5/15 + 9/15 + 1/15 ) – ( 27/36 + 8/36 + 1/36 ) + 1/72`

   `=  1 – 1 + 1/72`

   `=  0 + 1/72 = 1/72`

    

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