(1).(x+a)(x+b)
=x^2+(a+b)x+ab
(2).(3x+7y)(3x-7y)
=(3x)^2-(7y)^2
=9x^2-49y^2
(3).(3x+9)(6x+8)
=18x^2+78x+72
(4).(1/2x^2y-2xy+y^2)·3xy
=3/2x^3y^2-6x^2y^2+3xy^3
(5).(1/3a^2b^3)·(-15a^2b^2)
=-5a^4b^5
(6).(4a^3b-6a^2b^2+12ab^3)÷(2ab)
=2a^2-3ab+6b^2
(7).(a^2bc)^2÷(ab^2c)
=a^4b^2c^2÷ab^2c
=a^3c
(8).(3mn+1)(3mn-1)-8m^2n^2
=(3mn)^2-1-8m^2n^2
=m^2n^2-1
(9).[(3a+b)^2-b^2]÷a
=(9a^2+6ab)÷a
=8a+6b
(10).(x+2)^2-(x+1)(x-1)
=x^2+4x+4-x^2+1
=4x+5