Đáp án:
Giải thích các bước giải:
` a, x^2 -3x+2=0`
`<=> x^2 - x-2x+2=0`
`<=> x(x-1)-2(x-1)=0`
`<=> (x-1)(x-2)=0`
`<=> $\left \{ {{x-1=0} \atop {x-2=0}} \right.$`
`<=> $\left \{ {{x=1} \atop {x=2}} \right.$ `
`Vậy $\left \{ {{x=1} \atop {x=2}} \right.$ `
` b,-x^2+5x-6=0 `
`<=> -x^2+2x+3x-6=0`
`<=> ( -x^2+2x)+(3x-6)=0`
`<=> -x ( x-2 )+3(x-2)=0`
`<=> (3-x)(x-2)=0`
`<=> $\left \{ {{3-x=0} \atop {x-2=0}} \right.$ `
` <=> $\left \{ {{x=3} \atop {x=2}} \right.$ `
`Vậy $\left \{ {{x=3} \atop {x=2}} \right.$ `
`c,4x^2-12x+5=0`
`<=>4x^2-10x-2x+5=0`
`<=> (4x^2-10x)-(2x-5)=0`
`<=> 2x(2x-5)-(2x-5)=0`
`<=> (2x-1)(2x-5)=0`
`<=> $\left \{ {{2x-1=0} \atop {2x-5=0}} \right.$ `
`<=> $\left \{ {{x=1/2} \atop {x=5/2}} \right.$`
` Vậy $\left \{ {{x=1/2} \atop {x=5/2}} \right.$`
`d,2x^2+5x+3=0`
`<=>2x^2+2x+3x+3=0`
`<=> (2x^2+2x)+(3x+3)=0`
`<=> 2x(x+1)+3(x+1)=0`
`<=> (2x+3)(x+1)=0`
`<=> $\left \{ {{2x+3=0} \atop {x+1=0}} \right.$ `
`<=> $\left \{ {{x=(-3/2)} \atop {x=-1}} \right.$ `
`Vậy $\left \{ {{x=(-3/2)} \atop {x=-1}} \right.$ `
