Question

Решите тригонометрическое уравнение​

Answer 1

$\Big(6Cosx-\dfrac{2}{Cosx}\Big)^{3}=125tg^{3}x\\\\\Big(6Cosx-\dfrac{2}{Cosx}\Big)^{3}=(5tgx)^{3}\\\\6Cosx-\dfrac{2}{Cosx} =5tgx\\\\6Cosx-\dfrac{2}{Cosx} -\dfrac{5Sinx}{Cosx}=0 \ , \ Cosx\neq0\\\\6Cos^{2} x-5Sinx-2=0\\\\6(1-Sin^{2}x)-5Sinx-2=0\\\\6-6Sin^{2}x-5Sinx-2=0\\\\6Sin^{2}x+5Sinx-4=0\\\\Sinx=m \ , \ -1\leq m \leq 1\\\\6m^{2} +5m-4=0\\\\D=5^{2} -4\cdot 6\cdot (-4)=25+96=121=11^{2} \\\\m_{1}=\frac{-5+11}{12}=\frac{1}{2}$

$m_{2}=\frac{-5-11}{12}=-1\frac{1}{3} <-1-neyd\\\\Sinx=\frac{1}{2}\\\\x=(-1)^{n} arc Sin\frac{1}{2}+\pi n,n\in Z\\\\\boxed{x=(-1)^{n} \frac{\pi }{6} +\pi n,n\in Z}$