Đáp án+Giải thích các bước giải:
`A = x^2 +6x + 9 - y^2`
`= (x^2 + 2.x.3 + 3^2) - y^2`
`= (x+3)^2 - y^2`
`= (x+3-y)(x+3+y)`
`text{_____________________________________}`
`A=x^2 + 4x - y^2 + 4`
`= (x^2 + 4x + 4) - y^2`
`= (x+2)^2 - y^2`
`= (x+2-y)(x+2+y)`
`text{_____________________________________}`
`A=9-x^2 - 2xy - y^2`
`= 9-(x^2 + 2xy + y^2)`
`= 3^2 - ( x+y)^2`
`= (3-x-y)(3+x+y)`
`text{_____________________________________}`
`A = x^2 + 4x - y^2 + 4`
`= (x^2 + 4x + 4) - y^2`
`= (x+2)^2 - y^2`
`= (x+2-y)(x+2+y)`
`text{_____________________________________}`
`A = x^2 - y^2 + 4x + 4`
`= (x^2 + 4x + 4) - y^2`
`= (x+2)^2 - y^2`
`= (x+2-y)(x+2+y)`
`text{_____________________________________}`
`A=x^2 - 2xy + y^2 -1`
`= (x^2 - 2xy +y^2)-1`
`= (x-y)^2 - 1^2`
`= (x-y-1)(x-y+1)`
