`10. 12a^2b^2-3(a^2+b^2)^2`
`=3[4a^2b^2-(a^2+b^2)^2]`
`=3[2ab+(a^2+b^2)][2ab-(a^2+b^2)]`
`=3(2ab+a^2+b^2)(2ab-a^2-b^2)`
`=3(a^2+2ab+b^2)[-(a^2-2ab+b^2)]`
`=-3(a+b)^2(a-b)^2`
`11. 4x^2y^2-(x^2+y^2-a^2)^2`
`=[2xy+(x^2+y^2-a^2)][2xy-(x^2+y^2-a^2)]`
`=(2xy+x^2+y^2-a^2)(2xy-x^2-y^2+a^2)`
`=[(x^2+2xy+y^2)-a^2][-(x^2-2xy+y^2-a^2)]`
`=-[(x+y)^2-a^2)][(x-y)^2-a^2]`
`=-(x+y+a)(x+y-a)(x-y+a)(x-y-a)`