rụt gọn biểu thức (1/căn x – 3 – 1/căn x + 3 ) /3/căn x – 3

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1. `(1/(√(x – 3)) – 1/(√( x + 3)) ) ÷ 3/(√( x – 3))`

   `= (√(x + 3) – √(x- 3))/((x – 3)(x+3)) × (√(x-3))/3`

   `= (√(x + 3) – √(x-3))/(√(x+3)) × 1/3`

   `= (√(x + 3) – √(x – 3))/(3√(x-3))`

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2. `(1/(sqrt(x)-3) – (1/(sqrt(x)+3) ) : 3/(sqrt(x)-3)`

   ĐKXĐ : `x>= 0 ; x ne 9`

   `= (sqrt(x)+3-sqrt(x)+3)/((sqrt(x)-3)(sqrt(x)+3)) . (sqrt(x)-3)/3`

   `= 6/((sqrt(x)-3)(sqrt(x)+3)) . (sqrt(x)-3)/3 `

   `= 2/(sqrt(x)+3)`

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