Question

\(x-6\sqrt{x}+5=0\)

\(-x^4+5x^2+6=0\)

Answer 1

a. ĐKXĐ: \(x\ge0\)

Đặt \(\sqrt{x}=t\ge0\)

\(\Rightarrow t^2-6t+5=0\Rightarrow\left[{}\begin{matrix}t=1\\t=5\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}\sqrt{x}=1\\\sqrt{x}=5\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=1\\x=25\end{matrix}\right.\)

b.

Đặt \(x^2=t\ge0\)

\(\Rightarrow-t^2+5t+6=0\Rightarrow\left[{}\begin{matrix}t=-1< 0\left(loại\right)\\t=6\end{matrix}\right.\)

\(\Rightarrow x^2=6\Rightarrow x=\pm6\)