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

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

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

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

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

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

(10-m)*(10+m)=-2

(z-10)*(z+10)=2-

(10-cd)*(cd+10)=-()2

(9b-10)*(9b+10)=*2-

(9b-10)*(10+9b)=(*)2-

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

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

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

(10bc3-2x)*(2x+10bc3)=*b2c6-*2

(10bc3-2x)*(2x+10bc3)=(*bc3)2-*2



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