Пусть
<em>S - количество травы на лугу:</em>
<em>v - скорость роста травы;</em>
<em>V - скорость поедания травы одной коровой в день;</em>
<em>x - количество коров в третьем случае</em>
Тогда
![\begin{cases} S+24v=70*V*24 \\S+60v=30*V*60\\ S+96v=x*V*96 \end{cases}](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D+S%2B24v%3D70%2AV%2A24+%5C%5CS%2B60v%3D30%2AV%2A60%5C%5C+S%2B96v%3Dx%2AV%2A96+%5Cend%7Bcases%7D)
1. ![\begin{cases} S=60(30V-v) \\S=96(xV-v)\end{cases}](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D+S%3D60%2830V-v%29+%5C%5CS%3D96%28xV-v%29%5Cend%7Bcases%7D+)
![5(30V-v)=8(xV-v);](https://tex.z-dn.net/?f=5%2830V-v%29%3D8%28xV-v%29%3B)
...
![x=18,75+\frac{3}{8}\frac{v}{V}](https://tex.z-dn.net/?f=x%3D18%2C75%2B%5Cfrac%7B3%7D%7B8%7D%5Cfrac%7Bv%7D%7BV%7D)
2. ![\begin{cases} S=70V*24-24v \\S=30V*60-60v \end{cases}](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D+S%3D70V%2A24-24v+%5C%5CS%3D30V%2A60-60v+%5Cend%7Bcases%7D)
![\begin{cases} S=70V*24-24v \\S=30V*60-60v \end{cases}](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D+S%3D70V%2A24-24v+%5C%5CS%3D30V%2A60-60v+%5Cend%7Bcases%7D)
...
![\frac{v}{V}=\frac{10}{3}](https://tex.z-dn.net/?f=%5Cfrac%7Bv%7D%7BV%7D%3D%5Cfrac%7B10%7D%7B3%7D)
3.![x=18,75+\frac{3}{8}\frac{10}{3}=20](https://tex.z-dn.net/?f=x%3D18%2C75%2B%5Cfrac%7B3%7D%7B8%7D%5Cfrac%7B10%7D%7B3%7D%3D20)
Ответ:<em> 20 коров</em>
4у^2 - 36у - (у^2 + 2у -10у -30) = 4у^2 - 36у - у^2 - 2у +10у + 30= 3у^2 - 28у - 30
Как-то так
2X + 5Y = 178
Y + 12 = X
2*(Y + 12) + 5Y = 178
7Y = 154
Y = 22 ( пятирублевых монет)
X = 22 + 12 = 34 - двухрублевых монет
Проверка: 2*34 + 5*22 = 68 + 110 = 178
решено тебе удачи,пусть тебе поставить пятерку
-b/2+√D
x₁=-------------
a
-b/2-√D
x₂=--------------
a