Đáp án + Giải thích các bước giải:
a)
`3x^2 + 2x - 1 = 0`
`<=> 3x^2 + 3x - x - 1 = 0`
`<=> 3x . ( x + 1 ) - ( x + 1 ) = 0 `
`<=> ( 3x - 1 ) . ( x + 1 ) = 0`
`<=> 3x-1=0` or `x+1=0`
`<=> x=1/3` or `x=-1`
Vậy `S={-1;1/3}`
b)
`x^2 - 3x + 2 = 0 `
`<=> x^2 - 2x - x + 2 = 0`
`<=> x . ( x - 2 ) - ( x - 2 ) = 0 `
`<=> ( x - 1 ) . ( x - 2 ) =0`
`<=> x-1=0` or `x-2=0`
`<=> x=1` or `x=2`
Vậy `S={1;2}`
c)
`4x^2 - 12x + 5 = 0`
`<=> 4x^2 - 2x - 10x + 5 = 0`
`<=> 2x . ( 2x - 1 ) - 5 . ( 2x - 1 ) = 0 `
`<=> ( 2x - 5 ) . ( 2x - 1 ) = 0 `
`<=> 2x-5=0` or `2x-1=0`
`<=> x=5/2` or `x=1/2`
Vậy `S={5/2;1/2}`
d)
`x^2 + x - 2 = 0`
`<=> x^2 + 2x - x - 2 = 0`
`<=> x . ( x + 2 ) - ( x + 2 ) = 0 `
`<=> ( x - 1 ) . ( x + 2 ) = 0`
`<=> x-1=0` or `x+2=0`
`<=> x=1` or `x=-2`
Vậy `S={-2;1}`
