$\eqalign{
& 25 - 4{x^2} = 0 \to 4{x^2} = 25 \to {x^2} = \frac{{25}}{4} \to x = \pm \frac{5}{2} \cr
& {x^2} - 2x + 3 = 0 \to \Delta = 4 - 12 = - 8 \cr} $ ریشه حقیقی ندارد
$\begin{align*}
x - 2 &= 0 &\Rightarrow x &= 2 \\
2x^2 + 3x - 5 &= 0 \\
\Delta &= 49 \\
\begin{cases}
x_1 &= \frac{-3 - 7}{4} = \frac{-5}{2} \\
x_2 &= \frac{-3 + 7}{4} = \frac{4}{4} = 1
\end{cases}
\end{align*}$