Tìm x, biết: (a) 2(x−3)−4x=0. (b) (x−3)^2+(5−x)(5+x)=4.

a) \[2\left( {x - 3} \right) - 4x = 0\]

\[\begin{array}{l}2x - 6 - 4x = 0\\ - 2x = 6\\x = - 3\end{array}\]

Vậy \(x = - 3\)

b) \({\left( {x - 3} \right)^2} + \left( {5 - x} \right)\left( {5 + x} \right) = 4\)

\(\begin{array}{l}{\left( {x - 3} \right)^2} + \left( {5 - x} \right)\left( {5 + x} \right) = 4\\{x^2} - 6x + 9 + 25 - {x^2} = 4\\6x = 30\\x = 5\end{array}\)

Vậy \(x = 5\)