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( ). 1. , . 2. . 4- . - 4- 3 - 4- 2 . : 90 . , ? . 3 , , 90:3 = 30 . ( 4 , 304 = 120 ). 2 , 90:2 = 45 . ( 4 , 454 = 180 ). : , , , , . 4- . .