a2-b2=(a-b)(a+b)
(6-x)*(6+x)=-2
(a-6)*(a+6)=2-
(6-cd)*(6+cd)=-()2
(9b-6)*(9b+6)=*2-
(9b-6)*(9b+6)=(*)2-
(16-m)*(16+m)=-2
(z-16)*(z+16)=2-
(16-cd)*(cd+16)=-()2
(6b-16)*(6b+16)=*2-
(6b-16)*(16+6b)=(*)2-
(9ab-zx)*(zx+9ab)=*()2-()2
(9z+a)*(a-9z)=2-*2
(mlu+9k)*(9k-mlu)=*2-()2
(16bc3-9x)*(9x+16bc3)=*b2c6-*2
(16bc3-9x)*(9x+16bc3)=(*bc3)2-*2