76 + X + 45 = 121 + X
---------------------------
19 + 89 + X = 108 + X
X = 12
108 + 12 = 120
1 центнер = 100 кг
3ц 80 кг = 380 кг
60,2-49,41:(30-13,8)*6,9=39,155
1)30-13,8=16,2
2)49,41:16,2=3,05
3)3,05*6,9=21,045
4)60,2-21,045=39,155
<span> (1 28/63 - 17/21) * 7 7/8=5
1)1 28/63-17/21=91/63-51/63=40/63
2)40/63*7 7/8=40/63*63/8=40/8=5
</span>
<span>сtg(3x - π/6) = √3
3x - </span>π/6 = arcctg√3 + πn, n ∈ Z
3x - π/6 = π/6 + πn, n ∈ Z
3x = 2π/6 + πn, n ∈ z
3x = π/3 + πn, n ∈ Z
x = π/9 + πn/3, n ∈ Z
Отберем корни, принадлежащие отрезку <span>[-5π/2; -2π].
</span>при n = 0 х= π/9 ∉ <span>[-5π/2; -2π],
</span>при n = -1 х= π/9 - π/3 = π/9 - 3π/9 = -2π/9 ∉ <span>[-5π/2; -2π],
</span>при n = -2 х= π/9 - 2π/3 = π/9 - 6π/9 = -5π/9 ∉ <span>[-5π/2; -2π],
</span>при n = -3 х= π/9 - 3π/3 = π/9 - π = -8π/9 ∉ [-5π/2; -2π],
при n = -4 х= π/9 - 4π/3 =π/9 - 12π/9 = -11π/9 ∉ [-5π/2; -2π],
при n = -5 х= π/9 - 5π/3 = π/9 - 15π/9 = -14π/9 ∉ [-5π/2; -2π],
при n = -6 х= π/9 - 6π/3 = π/9 - 2π = -17π/9 ∉ [-5π/2; -2π],
при n = -7 х= π/9 - 7π/3 = π/9 - 21π/9 = -20π/9<span> </span>∈ [-5π/2; -2π],
при n = -8 х= π/9 - 8π/3 = π/9 - 24π/9 = -23π/9 ∉ [-5π/2; -2π],
<span>
</span>Ответ: -20π/9.