Tìm x biết:
\(a)\;{x^2} - 3x - 10 = 0\) \(b)\;7x\left( {3x - 2} \right) - 4 + 6x = 0\)
Giải chi tiết:
\(\eqalign{& a)\;{x^2} - 3x - 10 = 0 \cr & \Leftrightarrow {x^2} - 5x + 2x - 10 = 0 \cr & \Leftrightarrow x\left( {x - 5} \right) + 2\left( {x - 5} \right) = 0 \cr & \Leftrightarrow \left( {x + 2} \right)\left( {x - 5} \right) = 0 \cr & \Leftrightarrow \left[ \matrix{x + 2 = 0 \hfill \cr x - 5 = 0 \hfill \cr} \right. \Leftrightarrow \left[ \matrix{x = - 2 \hfill \cr x = 5 \hfill \cr} \right. \cr} \) \(\eqalign{& b)\;7x\left( {3x - 2} \right) - 4 + 6x = 0 \cr & \Leftrightarrow 7x\left( {3x - 2} \right) + 2\left( {3x - 2} \right) = 0 \cr & \Leftrightarrow \left( {7x + 2} \right)\left( {3x - 2} \right) = 0 \cr & \Leftrightarrow \left[ \matrix{7x + 2 = 0 \hfill \cr 3x - 2 = 0 \hfill \cr} \right. \Leftrightarrow \left[ \matrix{ x = - {2 \over 7} \hfill \cr x = {2 \over 3} \hfill \cr} \right. \cr}\)