easy maths(10m)

1) 16x^2 - 4y^2 + 12y - 9
=16x^2 -( 4y^2 - 12y + 9)
=(4x)^2-(2y-3)^2
=(4x-2y-3)(4x+2y-3)
2) x^2 - y^2 + 4x + 8y - 12
=x^2 + 4x+4-y^2 + 8y -16
=(x+2)^2-(y^2-8y+16)
=(x+2)^2-(y-4)^2
=(x+2-y+4)(x+2+y-4)
3) (5x - 3) (2x + 1) - 18
=10x^2+5x-6x-3-18
=10x^2-x-21
=(5x+7)(2x-3)