Tìm giá trị của xxx thỏa mãn:
(2x−3)(x+2)+(x+5)(4−x)=30\left( {2x - 3} \right)\left( {x + 2} \right) + \left( {x + 5} \right)\left( {4 - x} \right) = 30(2x−3)(x+2)+(x+5)(4−x)=30
x = 4
x = -4
x = 4; x = -4
x = 0; x = 4
Đáp án: <p>x = 4; x = -4</p>
Lời giải chi tiết:
(2x−3)(x+2)+(x+5)(4−x)=302x(x+2)−3(x+2)+x(4−x)+5(4−x)=302x2+4x−3x−6+4x−x2+20−5x=30(2x2−x2)+(4x−3x+4x−5x)+(20−6)=30x2+14=30x2=16\begin{array}{l}\left( {2x - 3} \right)\left( {x + 2} \right) + \left( {x + 5} \right)\left( {4 - x} \right) = 30\\ 2x\left( {x + 2} \right) - 3\left( {x + 2} \right) + x\left( {4 - x} \right) + 5\left( {4 - x} \right) = 30\\ 2{x^2} + 4x - 3x - 6 + 4x - {x^2} + 20 - 5x = 30\\ (2{x^2}- {x^2}) + (4x - 3x + 4x - 5x) + (20 - 6) = 30\\ {x^2} + 14 = 30\\ {x^2} = 16\end{array}(2x−3)(x+2)+(x+5)(4−x)=302x(x+2)−3(x+2)+x(4−x)+5(4−x)=302x2+4x−3x−6+4x−x2+20−5x=30(2x2−x2)+(4x−3x+4x−5x)+(20−6)=30x2+14=30x2=16
suy ra x=4x = 4x=4 hoặc x=−4x = - 4x=−4
Vậy x=4x = 4x=4; x=−4.x = - 4.x=−4.
