~ Bạn tham khảo ~
`a, x^2 + 3x - (2x + 6) = 0`
`<=> x(x+3) - 2(x+3) = 0`
`<=> (x+3)(x-2)=0`
`<=>[(x-2=0),(x+3=0):}`
`<=>[(x=2),(x=-3):}`
Vậy `x={2;-3}`
`b, 5x + 20 - x^2 - 4x = 0`
`<=> 5(x+4) - x(x+4) = 0`
`<=> (x+4)(5-x)=0`
`<=> -(x-5)(x+4)=0`
`<=>[(x-5=0),(x+4=0):}`
`<=>[(x=5),(x=-4):}`
Vậy `x={5;-4}`