`1)(x+2)^2+(3-x)^2`
`=(x^2+4x+4)+(9-6x+x^2)`
`=x^2+4x+4+9-6x+x^2`
`=(x^2+x^2)+(4x-6x)+(4+9)`
`=2x^2-2x+13`
`3)(x-5)(x+5)-(x+5)^2`
`=x^2-5^2-(x^2-10x+25)`
`=x^2-25-x^2+10x-25`
`=(x^2-x^2)+10x+(-25-25)`
`=10x-50`
`5)(y^2-6y+9)-(3-y)^2`
`=y^2-6y+9-(9-6y+y^2)`
`=y^2-6y+9-9+6y-y^2`
`=(y^2-y^2)+(-6y+6y)+(9-9)`
`=0`
$@ThanhTruc2008$
