`x^2-4x+2`
`=x^2-4x+4-2`
`=(x-2)^2-2`
`=(x-2-\sqrt{2})(x-2+\sqrt{2})`
`x^2-12+11`
`=x^2-12+36-25`
`=(x-6)^2-5^2`
`=(x-6+5)(x-6-5)`
`=(x-1)(x-11)=0`
..............
`3x^2+6x-9`
`=3(x^2+2x-3)`
`=3(x^2-x+3x-x)`
`=3[x(x-1)+3(x-1)]`
`=3(x+3)(x-1)`
.....
`2x^2-6x+2`
`=2x^2-6x+9/2-9/2+2`
`=2(x^2-3x+9/4)-5/2`
`=2(x-3/2)^2-5/2`
`=[2(x-3/2)-(\sqrt{5})/(\sqrt{2})][2(x-3/2)+(\sqrt{5})/(\sqrt{2})]`
