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

(7-x)*(7+x)=-2

(a-7)*(a+7)=2-

(7-cd)*(7+cd)=-()2

(9b-7)*(9b+7)=*2-

(9b-7)*(9b+7)=(*)2-

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

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

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

(7b-12)*(7b+12)=*2-

(7b-12)*(12+7b)=(*)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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