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):=26/36-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