(a-b)-(a+b)== a-b -a-b = -2b
(x²+y²)-(-x²-y²)=x^2+y^2 + x^2+y^2 = 2(x^2+y^2)
-(w²-v²)-(v²-w²)= -w^2+v^2-v^2+w^2 = 0
-(4-a)+(2a-7)-(-4a+6)= = -4+a + 2a-7 +4a-6 = -17+7a
xy(x-y)-y²(y-x)-3x=x^2*y-xy^2 - y^3+y^2*x-3x = -y^3+x^2*y-3x
-3pq+2q(p-q)-(p²+q²)= -3pq + 2pq-2q^2 - p^2-q^2 = -pq-3q^2-p^2
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