Question

How to find when sqrt(cosx) is undefined?

Answer 1

Ask: when is square root undefined?

Answer 2

exactly

Answer 3

Then figure out what values of x produce that for cos x.

Answer 4

the values of cosine vary between -1 to 1

Answer 5

Where is cos(x) undefindes -> Never
Sqrt -> x < 0

So, it is undefined for values where cos(x) < 0

Answer 6

I know that cosx >= 0. But unsure how to solve for x.

Answer 7

What if:
\[f:\mathbb{R}\rightarrow\mathbb{C}\](don't pay attention to me) ;p

Answer 8

cos x has to be greater than or equal to 0. You can look at the unit circle to see what angles yield negative cosines (i.e., wherever the unit circle is less than 0 on the x axis, meaning quadrants II and III).