... 12 .20: 4 cỏch; 8 cỏch. 12 . 21: Loi 3: 5, 10 , 15 cỏi v tng ng loi 5: 8, 5, 2 cỏi. 12 .22: loi (5, 3, 1/ 3) cú (4, 18 , 78) hoc (8, 11 , 81 ) hoc (12 , 4, 84 ) cỏi. 12 .23: 5 cỏi; 6 cỏi. Chng 13 : 13 .1: ... 2 .10 18 phõn t/cm3. 7.7: 5,74 atm; an ton. 7 .8: 1, 83 g/lớt. Chng 8: 8 .1: sinh cụng A =10 00J; nhn nhit Q = 2500J. 8. 2: sinh cụng A = 11 84 J; nhn nhit Q = 11 84 J. 8. 3: 30 ,8% . 8. 4: 2324J. 8. 5: ... 42m. 1. 18: b) t = 1/ ; =2rs0. 1. 19: = sin20. 1. 20: 30tb=. 1. 21: s = 85 m. 1. 22: t 1 = 0 ,89 4s; t 10 = 0 ,14 5s. 1. 23: s = At. 1. 24: a) = 3 ,14 rad/s; b) v = 1, 02 m/s; at = 1, 02...