12: Ta có: \(\sqrt{3x+5^2}=7\)

\(\Leftrightarrow3x+25=49\)

hay x=8

13: Ta có: \(\sqrt{x^2-10x+25}=4\)

\(\Leftrightarrow\left|x-5\right|=4\)

\(\Leftrightarrow\left[{}\begin{matrix}x-5=4\\x-5=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=9\\x=1\end{matrix}\right.\)

11: Ta có: \(\sqrt{2x-3}=7\)

\(\Leftrightarrow2x-3=49\)

\(\Leftrightarrow2x=52\)

hay x=26

14: Ta có: \(\sqrt{x^2-x+11}=x+2\)

\(\Leftrightarrow x^2+4x+4-x^2+x-11=0\)

\(\Leftrightarrow5x=7\)

hay \(x=\dfrac{7}{5}\)

\(\left\{{}\begin{matrix}x=5-y\\y\left(5-y\right)=4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x=1\\y=4\end{matrix}\right.\\\left\{{}\begin{matrix}x=4\\y=1\end{matrix}\right.\end{matrix}\right.\)

a) Thay m = -2 vào (P) ta có:

\(y=\left(-2-3\right)x+\left(-2\right).\\ \Leftrightarrow y=-5x-2.\)

i) + \(y=-5x-2.\)

\(Cho\) \(x=0.\Rightarrow y=-2.\)

\(Cho\) \(y=0.\Rightarrow x=\dfrac{-2}{5}.\)

+ \(y=2x^2.\)

Bài 5: 

a: Để đây là hàm số bậc nhất thì m+5<>0

hay m<>-5