Đúng r, mình nhầm
Cảm ơnn

x=-3 thì \(\sqrt{x+4}=\sqrt{-3+4}=\sqrt{1}>0\) mà c

d. \(\dfrac{x-2}{x-1}=\dfrac{x+4}{x+7}\)

\(\Rightarrow\left(x-2\right)\left(x+7\right)=\left(x-1\right)\left(x+4\right)\)

\(\Rightarrow x^2+5x-14=x^2+3x-4\)

\(\Rightarrow x^2+5x-x^2-3x=-4+14\)

\(\Rightarrow2x=10\) \(\Rightarrow x=\dfrac{10}{3}\) \(\Rightarrow x=5\)

Câu 3 ĐKXĐ đúng mà c, \(x^2\) thì cần gì phải xét vì \(x^2\) luôn lớn hơn hoặc bằng 0 mà

um, tớ quên xét 2TH

4. ĐKXĐ: \(x\ge-7\)

\(\sqrt{x^2-49}-3\sqrt{x+7}=0\)

\(\Leftrightarrow\sqrt{x^2-49}=3\sqrt{x+7}\)

\(\Leftrightarrow x^2-49=9\left(x+7\right)\)

\(\Leftrightarrow x-7=9\)

\(\Leftrightarrow x=16\) ( thỏa mãn đk )

Vậy \(S=\left\{16\right\}\)

5. ĐKXĐ: \(x\ge0\)

\(x-14\sqrt{x}+45=0\)

\(\Leftrightarrow\left(\sqrt{x}-9\right)\left(\sqrt{x}-5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-9=0\\\sqrt{x}-5=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=9\\\sqrt{x}=5\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=81\\x=25\end{matrix}\right.\)

Vậy \(S=\left\{81;25\right\}\)

6. ĐKXĐ: \(x\ge0\)

\(x-13\sqrt{x}+42=0\)

\(\Leftrightarrow\left(\sqrt{x}+6\right)\left(\sqrt{x}+7\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}+7=0\\\sqrt{x}+6=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=-7\\\sqrt{x}=-6\end{matrix}\right.\) ( loại )

Vậy phương trình vô nghiệm

Bài 1:

1. ĐKXĐ: \(x\ge0\) 
\(x-7\sqrt{x}+10=0\)

\(\Leftrightarrow x-2\sqrt{x}-5\sqrt{x}+10=0\)

\(\Leftrightarrow\sqrt{x}\left(\sqrt{x}-2\right)-5\left(\sqrt{x}-2\right)=0\)

\(\Leftrightarrow\left(\sqrt{x}-2\right)\left(\sqrt{x}-5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-2=0\\\sqrt{x}-5=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=2\\\sqrt{x}=5\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=25\end{matrix}\right.\) ( thỏa mãn đk )

Vậy \(S=\left\{4;25\right\}\)

2. ĐKXĐ: \(x\ge4\) 
\(\sqrt{x^2-16}-5\sqrt{x-4}=0\)

\(\Leftrightarrow\sqrt{x^2-16}=5\sqrt{x-4}\)

\(\Leftrightarrow x^2-16=25\left(x-4\right)\)

\(\Leftrightarrow x+4=25\)

\(\Leftrightarrow x=21\) ( thỏa mãn đk )

Vậy \(S=\left\{21\right\}\)

3. ĐKXĐ: \(x\ge-4\)
\(\sqrt{x^2-16}-3\sqrt{x+4}=0\)

\(\Leftrightarrow\sqrt{x^2-16}=3\sqrt{x+4}\)

\(\Leftrightarrow x^2-16=9\left(x+4\right)\)

\(\Leftrightarrow x-4=9\)

\(\Leftrightarrow x=13\) ( thỏa mãn đk )

Vậy \(S=\left\{13\right\}\)

1. She ___ four languages.

a. speak

b. speaks

2. Jane is a teacher. She ___ French.

a. teach

b. teaches

3. When the kettle ___, will you make some tea?

a. boil

b. boils

4. I always ___ the window at night because it is cold.

a. close

b. closes

5. Those shoes ___ too much.

a. cost

b. costs

6. The food in Japan is expensive. It ___ a lot to live there.

a. cost

b. costs

7. His job is great because he ___ a lot of people.

a. meet

b. meets