19. Calculaţi: a) [(7)¹¹.7³] [723 (6° +36¹2: 62³)]; c) [521: (1 +810:4¹4)¹9-1]: (4¹5: 89); 20. Calculati b) [(3-415: 810)17. 16²]: (2-2²4² d) [(7-25-87:4¹3): 3+1]4⁹: [(92)³​