a2-b2=(a-b)(a+b)
(5-x)*(5+x)=-2
(a-5)*(a+5)=2-
(5-cd)*(5+cd)=-()2
(8b-5)*(8b+5)=*2-
(8b-5)*(8b+5)=(*)2-
(13-m)*(13+m)=-2
(z-13)*(z+13)=2-
(13-cd)*(cd+13)=-()2
(5b-13)*(5b+13)=*2-
(5b-13)*(13+5b)=(*)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