Đáp án + giải thích các bước giải:
a) `\sqrt{x^2+6x+9}=2`
`->\sqrt{(x+3)^2}=2`
`->|x+3|=2`
`->`\(\left[ \begin{array}{l}x+3=2\\x+3=-2\end{array} \right.\)
`->`\(\left[ \begin{array}{l}x=-1\\x=-5\end{array} \right.\)
Vậy `S={-1;-5}`
b) `\sqrt{4x^2-10x+25}=7`
`->\sqrt{(2x-5)^2}=7`
`->|2x-5|=7`
`->`\(\left[ \begin{array}{l}2x-5=7\\2x-5=-7\end{array} \right.\)
`->`\(\left[ \begin{array}{l}2x=12\\2x=-2\end{array} \right.\)
`->`\(\left[ \begin{array}{l}x=6\\x=-1\end{array} \right.\)
Vậy `S={-1;6}`
c) `\sqrt{x^2-8x+16}=5`
`->\sqrt{(x-4)^2}=5`
`->|x-4|=5`
`->`\(\left[ \begin{array}{l}x-4=5\\x-4=-5\end{array} \right.\)
`->`\(\left[ \begin{array}{l}x=9\\x=-1\end{array} \right.\)
Vậy `S={-1;9}`
