Cos40 cos20-sin40 sin20=cos(40+20)= cos60=0,5
(1/5)x = 25
x= 25/(1/5)
x=(25*5)/1
x=125
![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
Первое уравнение умножим все на 2
6x-4y=14 теперь от него отнимем второе
-
6x-4y=1
=
(6x-6x)+(-4y-(-4y)=14-1
0 + 0 =13 решений нет
У=3*(-13/18) - 5
у=-13/6 - 5
у=-43/6
у=-7 1/6
-95=3х - 5
3х=-90
х=-30