7.
a)2(x²+y²)+a(x²+y²)=(x²+y²)(2+a)
b)3x²(y-z)+2a³(y-z)=(y-z)(3x²+2a³)
c)5xy(y-2x)+3x(y-2x)=(y-2x)(5xy+3x)=x(y-2x)(5y+3)
d)6x(x+2a)+5y²(x+2a)=(x+2a)(6x+5y²)
e)3ab(ab-1)+5c²(ab-1)=(ab-1)(3ab+5c²)
f)7x³(x-y)+8y³(x-y)=(x-y)(7x³+8y³)
4.
b)(3x+9-2)(3x+9+2)=(3x+7)(3x+11)
c)(4x-2-5)(4x-2+5)=(4x-7)(4x+3)
d)(12x-8-5x)(12x-8+5x)=(7x-8)(17x-8)
e)(x-2x+6)(x+2x-6)=(6-x)(3x-6)=3(6-x)(x-2)
f)(3x-3x-4)(3x+3x-4)=-4(6x-4)=-8(3x-2)
