1、(x-3y)(x-6y-1)；
=x²-6xy-x-3xy+18y²+3y
=x²-9xy+18y²-x+3y

2、(3a-b)(3a+b+5)；
=(3a-b)(3a+b)+5(3a-b)
=9a²-b²+15a-5b

3、(2x-1)(x²-x-1)
=2x³-2x²-2x-x²+x+1
=2x³-3x²-x+1

4、2x(x²-2x+3)-(x+5)(2x-3)；
=2x³-4x²+6x-(2x²+7x-15)
=2x³-6x²-x+15

5、3(2a+1)(2a-1)-4(3a-2)(3a+5).
=3(4a²-1）-4（9a²+9a-10)
=-24a²-36a+37