a2-b2=(a-b)(a+b)
(3-x)*(3+x)=-2
(a-3)*(a+3)=2-
(3-cd)*(3+cd)=-()2
(5b-3)*(5b+3)=*2-
(5b-3)*(5b+3)=(*)2-
(13-m)*(13+m)=-2
(z-13)*(z+13)=2-
(13-cd)*(cd+13)=-()2
(3b-13)*(3b+13)=*2-
(3b-13)*(13+3b)=(*)2-
(5ab-zx)*(zx+5ab)=*()2-()2
(5z+a)*(a-5z)=2-*2
(mlu+5k)*(5k-mlu)=*2-()2
(13bc3-5x)*(5x+13bc3)=*b2c6-*2
(13bc3-5x)*(5x+13bc3)=(*bc3)2-*2