1)(x+y)(x-y)=х²-у²
2)(n-m)(n+m)=n²-m²
3)(k-2)(k+2)=k²-4
4)(3-c)(3+c)=9-c²
5)(4+b)(4-b)=16-b²
6)(a-7)(a+7)=a²-49
7)(1/7+x)(1/7-x)=1/49-x²
8)(a-2/9)(a+2/9)=a²-4/81
9)(5/6-m)(5/6+m)=25/36-m²
10)(0,4+n)(0,4-n)=0.16-n²
11)(k+1,1)(k-1,1)=k²-1.21
12)(d-2,2)(d+2,2)=d²-4.84
