[tex]sec^2(x) \leq 4
\\\\ \frac{1}{cos^2(x)} \leq 4
\\\\ \frac{1}{cos^2(x)}-4\leq 0
\\\\ \frac{1-4cos^2(x)}{cos^2(x)} \leq 0
\\\\ 1-4cos^2(x)\leq 0*cos^2(x)
\\\\1-4cos^2(x) \leq 0
\\\\-4cos^2(x) \leq -1
\\\\cos^2(x) \leq \frac{-1}{-4}
\\ \\ cos^2(x)\geq \frac{1}{4}
\\ \\ \sqrt{cos^2(x)} \geq \sqrt{ \frac{1}{4}}
\\\\cos(x) \geq \frac{1}{2}
\\\\
x\geq60
\\-------------
\\\\ \theta_I=60
\\\\ \theta_{IV}=360-60
\\ \theta_{IV}=300[/tex]
60 ≤ x ≤ 300
or
[tex]60* \frac{ \pi }{180} = \frac{1}{3} \pi
\\ \\ 300*\frac{ \pi }{180} = \frac{5}{3} \pi [/tex]
[tex] \frac{1}{3} \pi \leq x \leq \frac{5}{3} \pi [/tex]
