Из ctg можно узнать tg, tg=1/ctg= -7
-7+4cos^2a+4sin^2a=-7+4(cos^2+sin^2)=-7+4*1=-3
cos^2+sin^2=1 по основному тригонометрическому свойству
D = 12*12+9*4*5 = 324
x1 = (12+18)/9*2 = 5/3 = 1 2/3
x2 = (12-18)/9*2 = -6/18 = -1/3
![e) \: \: \sin(x) = \cos(2x) \sin(x) \\ \\ \sin(x) - \cos(2x) \sin(x) = 0 \\ \\ \sin(x) \times (1 - \cos(2x) ) = 0 \\ \\ 1) \: \: \sin(x) = 0 \\ x = \pi \: n \\](https://tex.z-dn.net/?f=e%29+%5C%3A++%5C%3A+++%5Csin%28x%29++%3D++%5Ccos%282x%29++%5Csin%28x%29++%5C%5C++%5C%5C+%5Csin%28x%29+++-+++%5Ccos%282x%29++%5Csin%28x%29++%3D+0+%5C%5C++%5C%5C++%5Csin%28x%29++%5Ctimes+%281+-++%5Ccos%282x%29+%29+%3D+0+%5C%5C++%5C%5C+1%29+%5C%3A++%5C%3A++%5Csin%28x%29++%3D+0+%5C%5C++x+%3D+%5Cpi+%5C%3A+n+%5C%5C+)
n принадлежит Z
![2) \: \: \: 1 - \cos(2x) = 0 \\ \\ \cos(2x) = 1 \\ 2x = 2\pi \: k \\ x = \pi \: k \\](https://tex.z-dn.net/?f=2%29+%5C%3A++%5C%3A++%5C%3A+1+-++%5Ccos%282x%29++%3D+0+%5C%5C++%5C%5C++%5Ccos%282x%29++%3D+1+%5C%5C+2x+%3D+2%5Cpi+%5C%3A+k+%5C%5C+x+%3D+%5Cpi+%5C%3A+k+%5C%5C+)
k принадлежит Z
ОТВЕТ: пn , n принадлежит Z.