`3)(x^2+y^2-5)^2-4(x^2y^2+4xy+4)`
`=(x^2+y^2-5)^2-2^2(xy+2)^2`
`=(x^2+y^2-5)^2-(2xy+4)^2`
`=(x^2+y^2-5-2xy-4)(x^2+y^2-5+2xy+4)`
`=(x^2+y^2-2xy-9)(x^2+y^2+2xy-1)`
`=[(x-y)^2-9][(x+y)^2-1]`
`4)(x^2+y^2-z^2)^2-4x^2y^2`
`=(x^2+y^2-z^2)^2-(2xy)^2`
`=(x^2+y^2-z^2-2xy)(x^2+y^2-z^2+2xy)`
`=[(x-y)^2-z^2][(x+y)^2-z^2]`
`=(x-y-z)(x-y+z)(x+y-z)(x+y+z)`
`5)9x^2+90x+225-(x-7)^2`
`=(3x+15)^2-(x-7)^2`
`=(3x+15-x+7)(3x+15+x-7)`
`=(2x+22)(4x+8)`
`=8(x+11)(x+2)`