Question

Tìm ĐKXĐ của các biểu thức :

a) \(\sqrt{-3x+5}\)
b) \(\sqrt{\dfrac{5}{2x+7}}\)
c) \(\sqrt{\dfrac{-4x+12}{-8}}\)

Answer 1

a)ĐK:`-3x+5>=0`

`<=>5>=3x`

`<=>x<=5/3`

b)ĐK:`5/(2x+7)>=0(x ne -7/2)`

Mà `5>0`

`=>2x+7>0`

`<=>2x> -7`

`<=>x> -7/2`

c)ĐK:`(-4x+12)/(-8)>=0`

`<=>(-4(x-3))/(-4.2)>=0`

`<=>(x-3)/2>=0`

`<=>x-3>=0`

`<=>x>=3`

Answer 2

a, ĐKXĐ : \(\dfrac{-3x+5}{5}\ge0\)

\(\Leftrightarrow-3x+5\ge0\)

\(\Leftrightarrow x\le\dfrac{5}{3}\)

Vậy ..

b, ĐKXĐ : \(\left\{{}\begin{matrix}\dfrac{5}{2x+7}\ge0\\2x+7\ne0\end{matrix}\right.\)

\(\Leftrightarrow2x+7>0\)

\(\Leftrightarrow x>-\dfrac{7}{2}\)

Vậy ...

c, ĐKXĐ : \(\dfrac{-4x+12}{-8}\ge0\)

\(\Leftrightarrow-4x+12\le0\)

\(\Leftrightarrow x\ge3\)

Vậy ...