a) 2(x+5) - x2 - 5x = 0
\(\Leftrightarrow\) 2(x+5) - (x2+5x) = 0
\(\Leftrightarrow\) 2(x+5) - x(x+5) = 0
\(\Leftrightarrow\) (x+5)(2-x) = 0
\(\Leftrightarrow\) \(\left[\begin{array}{nghiempt}x+5=0\\2-x=0\end{array}\right.\) \(\Rightarrow\) \(\left[\begin{array}{nghiempt}x=-5\\x=2\end{array}\right.\)
Vậy x = -5 hoặc x = 2
b) 2x2 + 3x - 5 = 0
\(\Leftrightarrow\) 2x2 - 2x+5x - 5 = 0
\(\Leftrightarrow\) ( 2x2 - 2x ) + ( 5x - 5 ) = 0
\(\Leftrightarrow\) 2x(x - 1) + 5(x - 1) = 0
\(\Leftrightarrow\) (x - 1)(2x + 5) = 0
\(\Leftrightarrow\) \(\left[\begin{array}{nghiempt}x-1=0\\2x+5=0\end{array}\right.\) \(\Rightarrow\) \(\left[\begin{array}{nghiempt}x=1\\x=\frac{-5}{2}\end{array}\right.\)
Vậy x = 1 hoặc x = \(\frac{-5}{2}\)
