(1)(2x+1)(x+3)=2x^2+7x+3
(2)(a-b)(a^2+ab+b^2)+(b-a)(a^2+b^2)=(a-b)(a^2+ab+b^2)-(a-b)(a^2+b^2)
=(a-b)ab=a^2b-ab^2
(3)已知A=(a+2)(a-2),B=2(6-1/2a^2),求A+B的值
A+B=a^2-4+2(6-1/2a^2)=a^2-4+12-a^2=8
(4)(a-b)(a^2+b^2)(a^4+b^4)(a+b)
(5)已知x-y=40,y-z=25,x+z=30,求x^2-z^2的值
x-y+y-z=40+25 x-z=65 x^2-z^2=(x-z)(x+z)=30*65=1950