a2-b2=(a-b)(a+b)
(6-x)*(6+x)=-2
(a-6)*(a+6)=2-
(6-cd)*(6+cd)=-()2
(5b-6)*(5b+6)=*2-
(5b-6)*(5b+6)=(*)2-
(15-m)*(15+m)=-2
(z-15)*(z+15)=2-
(15-cd)*(cd+15)=-()2
(6b-15)*(6b+15)=*2-
(6b-15)*(15+6b)=(*)2-
(5ab-zx)*(zx+5ab)=*()2-()2
(5z+a)*(a-5z)=2-*2
(mlu+5k)*(5k-mlu)=*2-()2
(15bc3-5x)*(5x+15bc3)=*b2c6-*2
(15bc3-5x)*(5x+15bc3)=(*bc3)2-*2