Tìm x, biết: (a) 3(x^2−x)−3x^2−18=0

a) \(3\left( {{x^2} - x} \right) - 3{x^2} - 18 = 0\)

\(3{x^2} - 3x - 3{x^2} - 18 = 0\)

\( - 3x = 18\)

\(x = - 6\)

b) \({\left( {2x + 1} \right)^2} - 4{\left( {x - 1} \right)^2} = 17\)

\(4{x^2} + 4x + 1 - 4{x^2} + 8x - 4 = 17\)

\(12x = 20\)

\(x = \frac{5}{3}\)

c) \(16 - 4{(x + 1)^2} = 0\)

\(4{(x + 1)^2} = 16\)

\({(x + 1)^2} = 4\)

TH1: \(x + 1 = 2{\rm{\;}} \Rightarrow x = 1\)

TH2 \(x + 1 = - 2 \Rightarrow x = - 3\)

KL: \({\rm{\;}}x = 1; - 3\)