Ответ:
Пошаговое объяснение:
2) 20²-19² = (20-19)(20+19) = 1·39 = 39
4) 3,5²-3,7² = (3,5-3,7)(3,5+3,7) = -0,2·7,2 = -1,44
6) (7/9)²-(1/6)² = (7/9-1/6)(7/9+1/6) = (14/18-3/18)(14/18+3/18) = 11/18·17/18 = 187/324
8) (3/10)²-(4/5)² = (3/10)²-(8/10)² = (3/10-8/10)(3/10+8/10) = -5/10·11/10 = -11/20
10) (2 1/7)²-(2 1/7)² = 0
12) (5 1/6)²-(7 1/3)² = (5 1/6)²-(7 2/6)² = (5 1/6-7 2/6)(5 1/6+7 2/6) = -2 1/6·12 3/6 = -13/6·25/2 = -325/12 = -27 1/12
14) 54²-46² = (54-46)(54+46) = 8·100 = 800
16) 328²-172² = (328-172)(328+172) = 156·500 = 78000
18) (7 5/9)²-(4 4/9)² = (7 5/9-4 4/9)(7 5/9+4 4/9) = 3 1/9·12 = 37 1/3