TIM GTLL CUA BIEU THUC A a= √X – 2 chia X √X -8

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1. đkxđ: `x≥0; x\ne 4`

   `A=(\sqrtx-2)/[x\sqrtx-8]`

   `A=(\sqrtx-2)/[(\sqrtx-2)(x+2\sqrtx+4)]`

   `A=1/(x+2\sqrtx+4)`

   `A=1/[(\sqrtx+1)^2+3]`

   Vì `\sqrtx≥0`

   `⇒(\sqrtx+1)^2+3≥1+3=4`

   `⇒A=1/[(\sqrtx+1)^2+1]≤1/4`

   Dấu `=` xảy ra `⇔\sqrtx=0⇒x=0`

   Vậy $Max_A=\dfrac{1}{4}⇔=0$

    

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