a2-b2=(a-b)(a+b)
(6-x)*(6+x)=-2
(a-6)*(a+6)=2-
(6-cd)*(6+cd)=-()2
(8b-6)*(8b+6)=*2-
(8b-6)*(8b+6)=(*)2-
(13-m)*(13+m)=-2
(z-13)*(z+13)=2-
(13-cd)*(cd+13)=-()2
(6b-13)*(6b+13)=*2-
(6b-13)*(13+6b)=(*)2-
(8ab-zx)*(zx+8ab)=*()2-()2
(8z+a)*(a-8z)=2-*2
(mlu+8k)*(8k-mlu)=*2-()2
(13bc3-8x)*(8x+13bc3)=*b2c6-*2
(13bc3-8x)*(8x+13bc3)=(*bc3)2-*2