1)m²-(m+2)(m-3)
=m²-(m²-m-6)
=m²-m²+m-6
=m-6
2)(a-b)²+b(2a+b)
=a²-2ab+b²+2ab+b²
=a²+2b²
3)(x-3y)(y+3x)-(x-3y)(3y-x)
=(xy+3x²-3y²-9xy)+(x-3y)²
=3x²-3y²-8xy+x²+9y²-6xy
=4x²+6y²-14xy
4)(2x-y+3)(2x+y-3)
=[2x-(y-3)][2x+(y-3)]
=4x²-(y-3)²
=4x²-(y²-6y+9)
=4x²-y²+6y-9