Question 149438
What *[Tex \LARGE \cos^{-1}\left(0\right)] is asking for is an angle. So this means that *[Tex \LARGE \theta=\cos^{-1}\left(0\right)]. 


So, let's reference the unit circle


<img src="http://www1.fccj.edu/lchandouts/trigresources/Unit_circle_angles.png"></img>



From the picture, we can see that the point (0,1) tells us that {{{cos(90)=0}}} or {{{cos(pi/2)=0}}} (remember, the x coordinate corresponds to cosine). 



*[Tex \LARGE \cos\left(90\right)=0] Start with the given equation.



*[Tex \LARGE 90=\cos^{-1}\left(0\right)] Take the inverse cosine of both sides. This will eliminate the "cos" on the left side.



So *[Tex \LARGE \cos^{-1}\left(0\right)=90] (in degrees) or *[Tex \LARGE \cos^{-1}\left(0\right)=\frac{\pi}{2}] (in radians)