Toán Lớp 9: $\frac{1+ 3\sqrt{x}}{ \sqrt{x} -3}$ < 3
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Toán Lớp 9: $\frac{1+ 3\sqrt{x}}{ \sqrt{x} -3}$ < 3
Comments ( 2 )
<=>(1+3sqrtx)/(sqrtx-3)-3<0
<=>(1+3sqrtx)/(sqrtx-3)-(3(sqrtx-3))/(sqrtx-3)<0
<=>(1+3sqrtx-3(sqrtx-3))/(sqrtx-3)<0
<=>(1+3sqrtx-3sqrtx+9)/(sqrtx-3)<0
<=>10/(sqrtx-3)<0
Để 10/(sqrtx-3)<0
->10 và (sqrtx-3) trái đấu
Mà 10>0
->sqrtx-3<0->sqrtx<3->x<9
Vậy : 0<=x<9 thì (1+3sqrtx)/(sqrtx-3)<3