a2-b2=(a-b)(a+b)
(1-x)*(1+x)=-2
(a-1)*(a+1)=2-
(1-cd)*(1+cd)=-()2
(2b-1)*(2b+1)=*2-
(2b-1)*(2b+1)=(*)2-
(15-m)*(15+m)=-2
(z-15)*(z+15)=2-
(15-cd)*(cd+15)=-()2
(1b-15)*(1b+15)=*2-
(1b-15)*(15+1b)=(*)2-
(2ab-zx)*(zx+2ab)=*()2-()2
(2z+a)*(a-2z)=2-*2
(mlu+2k)*(2k-mlu)=*2-()2
(15bc3-2x)*(2x+15bc3)=*b2c6-*2
(15bc3-2x)*(2x+15bc3)=(*bc3)2-*2