3x^2-2x-5=0
D= b^2-4ac= 4+60= 64
x1,= 2+8/2= 5
x2= 2-8/2= -3
x1=5
x2=-3
p = m/n,
m = 30 - 5 = 25,
n = 30,
p = 25/30 = 5*5/(5*6) = 5/6.
V1-x
V2-4x
(4x-x)*2/3=35+5
8/3x-2/3x=40
2x=40:2
x=20(км/ч)-Vql1
4*20=80(км/ч)
![1) \: 2a + 7b = 20 \\ 2a = 20 - 7b \\ a = \frac{20 - 7b}{2} \\ a = 10 - 3.5b](https://tex.z-dn.net/?f=1%29+%5C%3A+2a+%2B+7b+%3D+20+%5C%5C+2a+%3D+20+-+7b+%5C%5C+a+%3D++%5Cfrac%7B20+-+7b%7D%7B2%7D++%5C%5C+a+%3D+10+-+3.5b)
![2) \: 2x + y = 18 \\ y = 18 - 2x](https://tex.z-dn.net/?f=2%29+%5C%3A+2x+%2B+y+%3D+18+%5C%5C+y+%3D+18+-+2x)
![- 0.2k = 8 \\ k + m = - 1 \\ \\ k = - 40 \\ - 40 + m = - 1 \\ \\ - 40 + m = - 1 \\ m = - 1 + 40 \\ m = 39](https://tex.z-dn.net/?f=+-+0.2k+%3D+8+%5C%5C+k+%2B+m+%3D++-+1+%5C%5C++%5C%5C+k+%3D++-+40+%5C%5C++-+40+%2B+m+%3D++-+1+%5C%5C++%5C%5C+-+40+%2B+m+%3D++-+1+%5C%5C+m+%3D++-+1+%2B+40+%5C%5C+m+%3D+39)
Ответ : k = -40 ; m=39
![x - y = 0 \\ x = \frac{1}{9} \\ \\ \frac{1}{9} - y = 0 \\ y = \frac{1}{9} - 0 \\ y = \frac{1}{9}](https://tex.z-dn.net/?f=x+-+y+%3D+0+%5C%5C+x+%3D++%5Cfrac%7B1%7D%7B9%7D++%5C%5C++%5C%5C++%5Cfrac%7B1%7D%7B9%7D++-+y+%3D+0+%5C%5C+y+%3D++%5Cfrac%7B1%7D%7B9%7D++-+0+%5C%5C+y+%3D++%5Cfrac%7B1%7D%7B9%7D+)
Ответ : х = 1/9 ; у = 1/9
(cos(105-75)-cos(105+75))/2=cos30-cos180=\/3/2+1
\/- корень
вроде так