Đề bài

Tính: a) \(\left( {2x + 5} \right)\left( {2x - 5} \right) - \left( {2x + 3} \right)\left( {3x - 2} \right)\) b) \({\left( {2x - 1} \right)^2} - 4\left( {x - 2} \right)\left( {x + 2} \right)\)

Lời giải chi tiết

a) \(\left( {2x + 5} \right)\left( {2x - 5} \right) - \left( {2x + 3} \right)\left( {3x - 2} \right)\)        \(\begin{array}{l} = \left( {4{x^2} - 25} \right) - \left( {6{x^2} - 4x + 9x - 6} \right)\\ = 4{x^2} - 25 - 6{x^2} + 4x - 9x + 6\\ =  - 2{x^2} - 5x - 19\end{array}\)

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

\(\begin{array}{l} = \left( {4{x^2} - 4x + 1} \right) - 4\left( {{x^2} - 4} \right)\\ = 4{x^2} - 4x + 1 - 4{x^2} + 16\end{array}\)

\( =  - 4x + 17\)