1. с/5b
2. 7/12x
3. 1,2 ( или 6/5)
4. 2y/3a
5.7y/4c
Cos²x + 2 sinx cosx - 3 sin²x = 0 | : cos²x
1 + 2 tgx - 3tg²x = 0 | * (-1)
3tg²x - 2tgx -1 = 0
Пусть tgx = t, тогда
3t² - 2t -1 = 0
D = b² - 4ac = 4 + 12 = 16
![x_{1} = \frac{2+4}{6}](https://tex.z-dn.net/?f=+x_%7B1%7D++%3D++%5Cfrac%7B2%2B4%7D%7B6%7D+)
![x_{1} = 1](https://tex.z-dn.net/?f=+x_%7B1%7D++%3D++1)
![x_{2} = \frac{2 - 4}{6}](https://tex.z-dn.net/?f=+x_%7B2%7D++%3D+++%5Cfrac%7B2+-+4%7D%7B6%7D+)
![x_{2} = \frac{-1}{3}](https://tex.z-dn.net/?f=+x_%7B2%7D++%3D++%5Cfrac%7B-1%7D%7B3%7D+)
Значит 1) tgx = 1
X =
![\frac{ \pi }{4}](https://tex.z-dn.net/?f=+%5Cfrac%7B+%5Cpi+%7D%7B4%7D+)
+
![\pi n](https://tex.z-dn.net/?f=+%5Cpi+n)
2) tgx = -
![\frac{1}{3}](https://tex.z-dn.net/?f=+%5Cfrac%7B1%7D%7B3%7D+)
x = - arctgx
![\frac{1}{3}](https://tex.z-dn.net/?f=+%5Cfrac%7B1%7D%7B3%7D+)
+
![\pi n](https://tex.z-dn.net/?f=+%5Cpi+n)
n ∈ Z
Решение
0,4*(- 15) - 10 = - 16
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