a2-b2=(a-b)(a+b)
(5-x)*(5+x)=-2
(a-5)*(a+5)=2-
(5-cd)*(5+cd)=-()2
(3b-5)*(3b+5)=*2-
(3b-5)*(3b+5)=(*)2-
(15-m)*(15+m)=-2
(z-15)*(z+15)=2-
(15-cd)*(cd+15)=-()2
(5b-15)*(5b+15)=*2-
(5b-15)*(15+5b)=(*)2-
(3ab-zx)*(zx+3ab)=*()2-()2
(3z+a)*(a-3z)=2-*2
(mlu+3k)*(3k-mlu)=*2-()2
(15bc3-3x)*(3x+15bc3)=*b2c6-*2
(15bc3-3x)*(3x+15bc3)=(*bc3)2-*2