(2a-5b)(2a^2-3ab+b^2)
=4a³-6a²b+2ab²-10a²b+15ab²-5b³
=4a³-16a²b+17ab²-5b³
（3x+2y)(2x+3y)-(x-3y)(3x+4y)
=(6x²+13xy+6y²)-(3x²-5xy-12y²)
=6x²+13xy+6y²-3x²+5xy+12y²
=3x²+18xy+18y²