Bài 1:
$\begin{array}{l} a)2{x^2} - 7x + 5 = 0\\ \Leftrightarrow 2{x^2} - 2x - 5x + 5 = 0\\ \Leftrightarrow 2x\left( {x - 1} \right) - 5\left( {x - 1} \right) = 0\\ \Leftrightarrow \left( {x - 1} \right)\left( {2x - 5} \right) = 0\\ \Leftrightarrow \left[ \begin{array}{l} x = 1\\ x = \dfrac{5}{2} \end{array} \right.\\ b)3{x^2} + 2{y^2} - 12x - 12y + 30 = 0\\ \Leftrightarrow \left( {3{x^2} - 12y + 12} \right) + 2{y^2} - 12y + 18 = 0\\ \Leftrightarrow 3\left( {{x^2} - 4x + 4} \right) + 2\left( {{y^2} - 6y + 9} \right) = 0\\ \Leftrightarrow 3{\left( {x - 2} \right)^2} + 2{\left( {y - 3} \right)^2} = 0\\ \Leftrightarrow \left[ \begin{array}{l} x = 2\\ y = 3 \end{array} \right. \end{array}$
