Đáp án:
Giải thích các bước giải:
a, $\left \{ {{3x-y=5} \atop {2x+3y=-4}} \right.$
⇔ $\left \{ {{y=5-3x} \atop {2x+3(5-3x)=-4}} \right.$
⇔$\left \{ {{y=5-3x} \atop {2x+15-9x=-4}} \right.$
⇔\(\left[ \begin{array}{l}x=\frac{-22}{7} \\x=\frac{19}{7}\end{array} \right.\)
b, 2x²+5x=0
⇔x(2x+5)
⇔\(\left[ \begin{array}{l}x=0\\2x+5=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=0\\x=$\frac{-5}{2}$ \end{array} \right.\)
c, 3x²-27=0
⇔3(x²-9)=0
⇔3(x-3)(x+3)=0
⇔\(\left[ \begin{array}{l}x-3=0\\x+3=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
