1) 8/21 + Х = 17/21
Х= 17/21 - 8/21
Х= 9/21
2) 48/56 -T =39/56
T = 48/56 - 39/56
T = 9/56
CosA=AC/AB
cosA=4/5............
X - 24 = 300 : 3 * 45 + 123
x - 24 = 100 * 45 + 123
x - 24 = 4500 + 123
x = 4623 + 24
x = 4647
Проверка
4647 - 24 = 300 : 3 * 45 + 123
4623 = 100 * 45 + 123
4623 = 4500 + 123
4623 = 4623