3 × ( x + 1 ) + 4 × ( x – 1 ) + 60 = 66

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1. `3 × (x + 1) + 4 × (x – 1) + 60 = 66`

   `3 × (x + 1) + 4 × (x – 1) = 66 – 60`

   `3 × (x + 1) + 4 × (x – 1) = 6`

   `(3 × x + 3 × 1) + (4 × x – 4 × 1) = 6`

   `(3 × x + 3) + (4 × x – 4) = 6`

   `3 × x + 3 + 4 × x – 4 = 6`

   `3 × x + 4 × x – (4 – 3) = 6`

   `x × (3 + 4) – 1 = 6`

   `x × 7 = 6 + 1`

   `x × 7 = 7`

   `x = 7 : 7`

   `x = 1`

   Vậy `x = 1`

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2. 3 x (X + 1) + 4 x (X – 1) + 60 = 66

   (3X + 3 x 1) + (4X – 4 x 1) = 66 – 60

   (3X + 3) + (4X – 4) = 6

   3X + 3 + 4X – 4 = 6

   3X + 4X = 6 – 3 + 4

   7X = 7

   X = 7 : 7

   X = 1

   Vậy X = 1

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