31.1. четные, 31.2. четные

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Объяснение:

31.1. 2) (n-m)(n+m) = n²-m²

4) (3-c)(3+c) = 9-c²

6) (a-7)(a+7) = a²-49

8) (a-2/9)(a+2/9) = a²-4/81

10) (0,4+n)(0,4-m) = 0,16-0,4m+0,4n-mn

12) (d-2,2)(d+2,2) = d²-4,84

31.2. 2) (8+y)(y-8) = y²-64

4) (a+2b/3)(a-2b/3) = a²-4b²/9

6) (4n/15-m)(m+4n/15) = 16n²/225-m²

8) (-4a+3b)(3b+4a) = 9b²-16a²

10) (5c/4+3d/7)(3d/7-5c/4) = 9d²/49-25c²/16

12) (a/5+b/9)(b/9-a/5) = b²/81-a²/25