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

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

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

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

(1b-7)*(1b+7)=*2-

(1b-7)*(1b+7)=(*)2-

(13-m)*(13+m)=-2

(z-13)*(z+13)=2-

(13-cd)*(cd+13)=-()2

(7b-13)*(7b+13)=*2-

(7b-13)*(13+7b)=(*)2-

(1ab-zx)*(zx+1ab)=*()2-()2

(1z+a)*(a-1z)=2-*2

(mlu+1k)*(1k-mlu)=*2-()2

(13bc3-1x)*(1x+13bc3)=*b2c6-*2

(13bc3-1x)*(1x+13bc3)=(*bc3)2-*2


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