a2-b2=(a-b)(a+b)
(9-x)*(9+x)=-2
(a-9)*(a+9)=2-
(9-cd)*(9+cd)=-()2
(8b-9)*(8b+9)=*2-
(8b-9)*(8b+9)=(*)2-
(19-m)*(19+m)=-2
(z-19)*(z+19)=2-
(19-cd)*(cd+19)=-()2
(9b-19)*(9b+19)=*2-
(9b-19)*(19+9b)=(*)2-
(8ab-zx)*(zx+8ab)=*()2-()2
(8z+a)*(a-8z)=2-*2
(mlu+8k)*(8k-mlu)=*2-()2
(19bc3-8x)*(8x+19bc3)=*b2c6-*2
(19bc3-8x)*(8x+19bc3)=(*bc3)2-*2