bài 2
1)   5x(1/5x - 2) + 3(6 - 1/3x^2)  = 12
<=> x^2 - 10x + 18x - x^2 = 12
<=> 18x = 22
<=> x = 11/9
2) 3x(4/3x + 1) - 4x(x - 2) = 10
<=> 4x^2 + 3x - 4x^2 + 8x = 10
<=> 11x = 10
<=> x = 10/11
5) 4x(x - 5) - 7x(x - 4) + 3x^2 = 12
<=> 4x^2 - 20x - 7x^2 + 28x + 3x^2= 12
<=>  8x = 12
<=> x = 3/2
6) 4x^2 - 2x + 3 - 4x(x - 5) = 7x - 3
<=> 4x^2 - 2x + 3 - 4x^2 + 20x = 7x - 3
<=> 11x = -6
<=> x = -6/11
7) -3x(x - 5) + 5(x - 1) + 3x^2 = 4 - x
<=> -3x^2 + 15x + 5x - 5 + 3x^2 = 4 - x
<=>  21x = 9
<=> x = 3/7