Answer:
b) \(2\sqrt{x+3}=9x^2-x-4\)
ĐK: x\(x\ge-3\) phương trình tương đương:
Ta có: \(2\sqrt{x+3}=9x^2-x-4\)
\(\Leftrightarrow x+4+2\sqrt{x+3}=9x^2\)
\(\Leftrightarrow x+3+2\sqrt{x+3}+1=9x^2\)
\(\Leftrightarrow\left(1+\sqrt{3+x}\right)^2=9x^2\)
\(\left(1+\sqrt{3+x}\right)^2=9x^2\)
\(\Leftrightarrow\orbr{\begin{cases}\sqrt{x+3}+1=3x\\\sqrt{x+3}+1=-3x\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=1\\x=\frac{-5-\sqrt{97}}{18}\end{cases}}\)