1)
<=> -3x - 7x = -24 - 12
<=> -10x = -36
<=> x = 18/5
2)
<=> 3x - 3 - 2x - 6 = -15
<=> x- 9 = -15
<=> x = -15 + 9
<=> x = -6
3)
<=> 9x^2 - 12x + 4 = 8x + 10 - 12x^2 - 15x
<=> 9x^2 - 12x + 4 = -7x + 10 - 12x^2
<=> 9x^2 - 12x + 4 + 7x - 10 + 12x^2
<=> 21x^2 - 5x - 6 = 0
<=> 21x^2 + 9x - 14x - 6 = 0
<=> 3x ( 7x + 3) - 2 ( 7x + 3) = 0
<=> ( 7x + 3) ( 3x - 2) = 0
Th1 : 7x + 3 = 0
x = -3/7
TH2 : 3x - 2 = 0
x = 2/3
4)
<=> 9x^2 - 6x + 1 - 9x^2 + 18x = 13
<=> 12x + 1 = 13
<=> 12x = 13 - 1
<=> 12x = 12
<=> x = 1
5)
Th1 : x^2 + 4 = 0
x không thuộc R
Th2 : 7x -3 = 0
x = 3/7