Answer:
[tex]x=\frac{3\pi}{4}\\\\x=\frac{5\pi}{4}[/tex]
Step-by-step explanation:
Trigonometric Equations
It's required to solve:
[tex]\cos x+\sqrt{2}=-\cos x[/tex]
for [tex]x\in [0,2\pi)[/tex]
Adding cos x:
[tex]2\cos x+\sqrt{2}=0[/tex]
Subtracting [tex]\sqrt{2}[/tex]
[tex]2\cos x=-\sqrt{2}[/tex]
Dividing by 2:
[tex]\displaystyle \cos x=-\frac{\sqrt{2}}{2}[/tex]
Solving for x:
[tex]\displaystyle x=\arccos\left(-\frac{\sqrt{2}}{2}\right)[/tex]
We need to find the angles whose cosine is [tex]-\frac{\sqrt{2}}{2}[/tex] over the given interval.
These angles lie on the quadrants III and IV respectively and they are:
x=135°, x=225°
Converting to radians:
135 * π / 180 = 3π/4
225 * π / 180 = 5π/4
The two solutions are:
[tex]\mathbf{x=\frac{3\pi}{4}}[/tex]
[tex]\mathbf{x=\frac{5\pi}{4}}[/tex]
