a2-b2=(a-b)(a+b)
(9-x)*(9+x)=-2
(a-9)*(a+9)=2-
(9-cd)*(9+cd)=-()2
(4b-9)*(4b+9)=*2-
(4b-9)*(4b+9)=(*)2-
(2-m)*(2+m)=-2
(z-2)*(z+2)=2-
(2-cd)*(cd+2)=-()2
(9b-2)*(9b+2)=*2-
(9b-2)*(2+9b)=(*)2-
(4ab-zx)*(zx+4ab)=*()2-()2
(4z+a)*(a-4z)=2-*2
(mlu+4k)*(4k-mlu)=*2-()2
(2bc3-4x)*(4x+2bc3)=*b2c6-*2
(2bc3-4x)*(4x+2bc3)=(*bc3)2-*2