Đáp án:
c) \(\left[ \begin{array}{l}
x = 1\\
x = - 1\\
x = 2\\
x = - 2
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
c){x^4} - 5{x^2} + 4 = 0\\
Dat:{x^2} = t\left( {t \ge 0} \right)\\
Pt \to {t^2} - 5t + 4 = 0\\
\to \left( {t - 1} \right)\left( {t - 4} \right) = 0\\
\to \left[ \begin{array}{l}
t = 1\\
t = 4
\end{array} \right.\\
\to \left[ \begin{array}{l}
{x^2} = 1\\
{x^2} = 4
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 1\\
x = - 1\\
x = 2\\
x = - 2
\end{array} \right.
\end{array}\)
\(\begin{array}{l}
a)3{x^2} - 4x - 2 = 0\\
\Delta ' = 4 - 3.\left( { - 2} \right) = 10\\
\to \left[ \begin{array}{l}
x = \dfrac{{2 + \sqrt {10} }}{3}\\
x = \dfrac{{2 - \sqrt {10} }}{3}
\end{array} \right.\\
b)DK:x \ge 0;y \ge 0\\
\left\{ \begin{array}{l}
3\sqrt x - 2\sqrt y = - 1\\
2\sqrt x + \sqrt y = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
3\sqrt x - 2\sqrt y = - 1\\
4\sqrt x + 2\sqrt y = 8
\end{array} \right.\\
\to \left\{ \begin{array}{l}
7\sqrt x = 7\\
2\sqrt x + \sqrt y = 4
\end{array} \right.\\
\to \left\{ \begin{array}{l}
\sqrt x = 1\\
\sqrt y = 2
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = 1\\
y = 4
\end{array} \right.
\end{array}\)
