Tính A = `(3/4 – 1/11 + 3/13)/(5/7 – 5/11 + 5/13) + (1/2 – 1/3 + 1/4)/(5/4 – 5/6 + 5/8)`

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1. Đáp án:

    `A=1`

   Giải thích các bước giải:

   * đề sai nên mk xin sửa lại thành :

   `A=(3/7- 3/11 + 3/13)/(5/7 – 5/11 + 5/13) + (1/2 – 1/3 + 1/4)/(5/4 – 5/6 + 5/8)`

   * bài làm như sau ạ :

   `A=(3/7 – 3/11 + 3/13)/(5/7 – 5/11 + 5/13) + (1/2 – 1/3 + 1/4)/(5/4 – 5/6 + 5/8)`

   `=(3(1/7-1/11+1/13))/(5(1/7-1/11+1/13)) + (1/2 – 1/3 + 1/4)/(5(1/4-1/6+1/8))`

   `=(3(1/7-1/11+1/13))/(5(1/7-1/11+1/13)) + (2/4- 2/6 + 2/8)/(5(1/4-1/6+1/8))`

   `=(3(1/7-1/11+1/13))/(5(1/7-1/11+1/13)) + (2(1/4-1/6+1/8))/(5(1/4-1/6+1/8))`

   `=(3(1/7-1/11+1/13))/(5(1/7-1/11+1/13)) + 2/5`

   `=3/5+2/5`

   `=1`

   vậy `A=1`

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2. Sửa đề: $A=\dfrac{\dfrac34-\dfrac3{11}+\dfrac3{13}}{\dfrac54-\dfrac5{11}+\dfrac5{13}}+\dfrac{\dfrac12-\dfrac13+\dfrac14}{\dfrac54-\dfrac56+\dfrac58}$

   $=\dfrac{3\bigg(\dfrac14-\dfrac1{11}+\dfrac1{13}\bigg)}{5\bigg(\dfrac14-\dfrac1{11}+\dfrac1{13}\bigg)}+\dfrac{2\bigg(\dfrac14-\dfrac16+\dfrac18\bigg)}{5\bigg(\dfrac14-\dfrac16+\dfrac18\bigg)}$

   $=\dfrac35+\dfrac25=1$

    

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