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Solve the equation for 0. Select all the values that apply -2√2=4 cos 0

 Apr 5, 2021
 #1
avatar+423 
+1

I am assuming you want $\theta$ not $0$.

 

We have that $\cos\theta=\frac{-2\sqrt{2}}{4}=-\frac{\sqrt{2}}{2}$. Use the fact that $\cos^{-1}\left(-\frac{\sqrt{2}}{2}\right)=\frac{3\pi}{4}$ and the fact that the period of $\cos x$ is $2\pi$ to finish.

 Apr 5, 2021
 #2
avatar+31353 
+1

......   and   5 pi/4

 Apr 5, 2021
 #3
avatar+423 
+1

Right, others besides just $\frac{3\pi}{4}$ work. I was just giving an example, because the rest follow from the period $2\pi$. In fact, the general solution is $\theta=2\pi n\pm \frac{3\pi}{4}$ for integer $n$.

 #4
avatar+31353 
+1

.....well. yah     and    2pi n  + 5pi/4

ElectricPavlov  Apr 5, 2021

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