a2-b2=(a-b)(a+b)
(5-x)*(5+x)=-2
(a-5)*(a+5)=2-
(5-cd)*(5+cd)=-()2
(9b-5)*(9b+5)=*2-
(9b-5)*(9b+5)=(*)2-
(2-m)*(2+m)=-2
(z-2)*(z+2)=2-
(2-cd)*(cd+2)=-()2
(5b-2)*(5b+2)=*2-
(5b-2)*(2+5b)=(*)2-
(9ab-zx)*(zx+9ab)=*()2-()2
(9z+a)*(a-9z)=2-*2
(mlu+9k)*(9k-mlu)=*2-()2
(2bc3-9x)*(9x+2bc3)=*b2c6-*2
(2bc3-9x)*(9x+2bc3)=(*bc3)2-*2