a(b+3) + b(a+3) - 3(a+b)=ab+3a+ab+3b-3a-3b=2ab
2(x-y) + 6(y-x) - (4x - 4y)=2x-2y+6y-6x-4x+4y=-8x+8y
a(b+c) - b(a+c) - c(a+b)=ab+ac-ab-bc-ac-bc=-2bc
m(n-l) + n(l-m) + l(m-n)=mn-ml+nl-mn+ml-nl=0
a(b+3) + b(a+3) - 3(a+b)=ab+3a+ab+3b-3a-3b=2ab
2(x-y) + 6(y-x) - (4x - 4y)=2x-2y+6y-6x-4x+4y=-8x+8y
a(b+c) - b(a+c) - c(a+b)=ab+ac-ab-bc-ac-bc=-2bc
m(n-l) + n(l-m) + l(m-n)=mn-ml+nl-mn+ml-nl=0