a2-b2=(a-b)(a+b)

(9-x)*(9+x)=-2

(a-9)*(a+9)=2-

(9-cd)*(9+cd)=-()2

(9b-9)*(9b+9)=*2-

(9b-9)*(9b+9)=(*)2-

(12-m)*(12+m)=-2

(z-12)*(z+12)=2-

(12-cd)*(cd+12)=-()2

(9b-12)*(9b+12)=*2-

(9b-12)*(12+9b)=(*)2-

(9ab-zx)*(zx+9ab)=*()2-()2

(9z+a)*(a-9z)=2-*2

(mlu+9k)*(9k-mlu)=*2-()2

(12bc3-9x)*(9x+12bc3)=*b2c6-*2

(12bc3-9x)*(9x+12bc3)=(*bc3)2-*2



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