a2-b2=(a-b)(a+b)
(2-x)*(2+x)=-2
(a-2)*(a+2)=2-
(2-cd)*(2+cd)=-()2
(1b-2)*(1b+2)=*2-
(1b-2)*(1b+2)=(*)2-
(5-m)*(5+m)=-2
(z-5)*(z+5)=2-
(5-cd)*(cd+5)=-()2
(2b-5)*(2b+5)=*2-
(2b-5)*(5+2b)=(*)2-
(1ab-zx)*(zx+1ab)=*()2-()2
(1z+a)*(a-1z)=2-*2
(mlu+1k)*(1k-mlu)=*2-()2
(5bc3-1x)*(1x+5bc3)=*b2c6-*2
(5bc3-1x)*(1x+5bc3)=(*bc3)2-*2