1) a) 7a+9b+3b-5a-6b+b=
=2a+7b
b) 4xy+7x-5xy-2x=
=-xy+5x
d) abc-bc+2abc+3bc-4abc=-abc+2bc
2)a) (2y+z)-(z-2y)= 2y+z-z+2y=4y
v) (2a-1)+(3-4a)=2a-1+3-4a=-2a+2
d)3m-(2m-3)+(2-m)=3m-2m+3+2-m=5
3)a) b(m-7)-7b=bm-7b-7b=bm-14b
v) y(x-4)+x(3x-y)=yx-4y+3x^2-xy=3x^2-4y
d) a(1-b)-a(1+b)=a-ab-a-ab=-2ab