Câu 5: B

Câu 3:

a: ĐKXĐ: \(\left\{{}\begin{matrix}x>=0\\x\ne4\end{matrix}\right.\)

b: \(P=\left(\dfrac{\sqrt{x}}{\sqrt{x}-2}+\dfrac{\sqrt{x}}{\sqrt{x}+2}\right):\dfrac{2\sqrt{x}}{x-4}\)

\(=\dfrac{\sqrt{x}\left(\sqrt{x}+2\right)+\sqrt{x}\left(\sqrt{x}-2\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}\cdot\dfrac{x-4}{2\sqrt{x}}\)

\(=\dfrac{x+2\sqrt{x}+x-2\sqrt{x}}{x-4}\cdot\dfrac{x-4}{2\sqrt{x}}\)

\(=\dfrac{2x}{2\sqrt{x}}=\sqrt{x}\)

c: Để P>4 thì \(\sqrt{x}>4\)

=>x>16

\(x-\sqrt{1-x}=\sqrt{x-2}+3\)

\(ĐK:\left\{{}\begin{matrix}1-x\ge0\\x-2\ge0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\le1\\x\ge2\end{matrix}\right.\Leftrightarrow x\in\varnothing\)

Vậy PT vô nghiệm

\(\Leftrightarrow x+9=49\)

hay x=40

ĐK x khác 0

X=-2

\(\sqrt{x+9}=7\)

Đk: \(x+9\ge0\Leftrightarrow x\ge-9\)

Pt\(\Rightarrow x+9=49\Rightarrow x=40\left(tmđk\right)\)

a: ĐKXĐ: x>=0; x<>1

b \(A=\left(\dfrac{2\sqrt{x}+x}{x\sqrt{x}-1}-\dfrac{1}{\sqrt{x}-1}\right):\dfrac{\sqrt{x}+2}{x+\sqrt{x}+1}\)

\(=\dfrac{x+2\sqrt{x}-x-\sqrt{x}-1}{x\sqrt{x}-1}\cdot\dfrac{x+\sqrt{x}+1}{\sqrt{x}+2}\)

\(=\dfrac{1}{\sqrt{x}+2}\)

c: Khi x=9-4 căn 5 thì \(A=\dfrac{1}{\sqrt{5}-2+2}=\dfrac{\sqrt{5}}{5}\)

d: căn x+2>=2

=>A<=1/2

Dấu = xảy ra khi x=0

ĐKXD : \(\sqrt{\frac{2}{3}x-\frac{1}{5}}\ge0\)

\(\Leftrightarrow\frac{2}{3}x-\frac{1}{5}\ge0\)

\(\Leftrightarrow\frac{2}{3}x\ge\frac{1}{5}\\ \Leftrightarrow x\ge\frac{3}{10}\)

Để căn thức \(\sqrt{\dfrac{2x+1}{x^2+1}}\) có nghĩa thì:

\(\left\{{}\begin{matrix}\dfrac{2x+1}{x^2+1}\ge0\\x^2+1\ne0\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}2x+1\ge0\left(vì.x^2+1>0\forall x\right)\\x^2+1\ne0\forall x\end{matrix}\right.\)

\(\Rightarrow2x\ge-1\Leftrightarrow x\ge-\dfrac{1}{2}\)

#\(Toru\)

\(\sqrt{\dfrac{2x+1}{x^2+1}}\)

Có nghĩa khi:

\(\dfrac{2x+1}{x^2+1}\ge0\)

\(\Leftrightarrow2x+1\ge0\)

\(\Leftrightarrow2x\ge-1\)

\(\Leftrightarrow x\ge-\dfrac{1}{2}\)

Vậy: ...