1. a) 2x+3x+7x=x (2+3+7)= 12x
b) 2ab-3ab+5ab= ab(2-3+5)=4ab
c)7x^2y*3xy^2=21x^2y^2
d)36x^2y:(-6x)= -6xy
2. (2+x)^2=2^2+2*2*x+x^2=4+4x+x^2
(x-7)^2=x^2-2*x*7+7^2=x^2-14x+49
(3x+1)(3x-1)=(3x)^2-1^2=9x^2-1
3. a) 3x+3y+3z=3(x+y+z)
b) 3x(y+2)+5(y+2)=(y+2)(3x+5)
c)x^2-10x+25=x^2-2*5*x+5^2=(x-5)^2
d)x^2-81=x^2-9^2=(x-9)(x+9)
e) x^2+12x+36=x^2+2*x*6+6^2=(x+6)^2
