`A = 81 . [ (12-12/7-12/289-12/85)/(4-4/7-4/289-4/5) : (5+5/13+5/169+5/91)/(6+6/13+6/169+6/91) ] - (158158158)/(711711711)`

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Bạn chép lại biểu thức `A`

$=81.(\dfrac{12 (1-\dfrac{1}{7}-\dfrac{1}{289}-\dfrac{1}{85}}{4(1-\dfrac{1}{7}-\dfrac{1}{289}-\dfrac{1}{5}} . \dfrac{6(1+\dfrac{1}{13}+\dfrac{1}{169}+\dfrac{1}{91}}{5(1+\dfrac{1}{13}+\dfrac{1}{169} +\dfrac{1}{91}})-\dfrac{2}{9}\\=81 . (\dfrac{12}{4}.\dfrac{6}{5}) - \dfrac{2}{9}\\=81 . \dfrac{18}{5}-\dfrac{2}{9}\\=\dfrac{1458}{5}-\dfrac{2}{9}\\=\dfrac{13112}{45}$

Vậy $A=\dfrac{13112}{45}$