`a,9x^2 – 49 = 0`
`<=>9x^2=49`
`<=>x^2=49/9`
`<=>x=+-` $\sqrt[]{\frac{7}{3}}$
`b) (x + 3)(x2 – 3x + 9) –x(x – 1)(x + 1) – 27 = 0`
`<=>x^3-3x^2+9x+3x^2-9x+27-x^3-x^2+x^2+x-27=0`
`<=>x=0`
`c)(x – 1)(x + 2) – x – 2 = 0`
`<=>(x+2)(x-1-1)=0`
`<=>x=+-2`
`d, x(3x + 2) + (x + 1)2 – (2x – 5)(2x + 5) = 0`
`<=>3x^2+2x+2x+2-4x^2+5^2=0`
`<=>-x^2+4x+27=0`
`<=>x=2-√32` hoặc `2+√31`
`d,(4x + 1)(x - 2) - (2x -3)(2x + 1) = 7`
`<=>4x^2-8x+x-2-4x^2-2x+6x+3=7`
`<=>-3x+1=7`
`<=>x=-2`