Advertisements (Quảng cáo)
Giải các phương trình sau:
a) \(2{x^2} + 3x = 0\)
b) \({x^2} – 2x – 15 = 0\)
c) \(4{x^2} – 9 = 0\)
Advertisements (Quảng cáo)
\(\begin{array}{l}a)\;2{x^2} + 3x = 0\\ \Leftrightarrow x\left( {2x + 3} \right) = 0\\ \Leftrightarrow \left[ \begin{array}{l}x = 0\\2x + 3 = 0\end{array} \right.\\ \Leftrightarrow \left[ \begin{array}{l}x = 0\\x = – \dfrac{3}{2}\end{array} \right.\end{array}\)
\(\begin{array}{l}b)\;{x^2} – 2x – 15 = 0\\ \Leftrightarrow {x^2} – 5x + 3x – 15 = 0\\ \Leftrightarrow x\left( {x – 5} \right) + 3\left( {x – 5} \right) = 0\\ \Leftrightarrow \left( {x – 5} \right)\left( {x + 3} \right) = 0\\ \Leftrightarrow \left[ \begin{array}{l}x – 5 = 0\\x + 3 = 0\end{array} \right.\\ \Leftrightarrow \left[ \begin{array}{l}x = 5\\x = – 3\end{array} \right.\end{array}\)
\(\begin{array}{l}c)\;4{x^2} – 9 = 0\\ \Leftrightarrow {\left( {2x} \right)^2} – {3^2} = 0\\ \Leftrightarrow \left( {2x – 3} \right).\left( {2x + 3} \right) = 0\\ \Leftrightarrow \left[ \begin{array}{l}2x – 3 = 0\\2x + 3 = 0\end{array} \right.\\ \Leftrightarrow \left[ \begin{array}{l}x = \dfrac{3}{2}\\x = – \dfrac{3}{2}\end{array} \right.\end{array}\)