Ответ на фото////////////
а) x^2 + 2x - 35 = 0
D = 2^2 - 4*1*(-35) = 144
X1 = -2 +12/2*1 = 5
X2 = -2-12/2*1 = -7
б) 3x^2 + x -2 = 0
D = 1^2 - 4*3*(-2) = 25
X1 = -1 + 5/2*3 = 2/3
X2 = -1 - 5/2*3 = -1
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>
3x² - 2xy -6xy -4y² = 3x² - 8xy - 4y²