Đáp án:
`x^2 - x - 6 = 0`
`=> x^2 - 2.x.1/2 + 1/4 - 1/2 -6`
`=> [x^2 -2.x.1/2 + (1/2)^2] - 1/2 -6`
`=> (x + 1/2 )^2 - 13/2`
`=> [(x + 1/2 )^2 - (√26)/2^2]`
`=> (x+ 1/2 - √26/2) (x + 1/2 + √26/2)=0`
`=> [x + (1-√26/2)].[x + (1+√26/2]=0`
`=> (x - 2 )(x + 3) = 0`
th1 :
`x-2 =0`
`=> x= 2`
th2
`x+3=0`
`=>x = -3`
`=> S ={2; -3}`
mong ctlhn ạ~~
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