(1)(x²-y²)-3(2x²-3y²)
=x²-y²-6x²+9y²
=-5x²+8y²
(2)7a²b-(-4a²b+5ab²)-2(2a²b-3ab²)
=7a²b+4a²b-5ab²-4a²b+6ab²
=7a²b+ab²