Which quadrants should be considered when solving #cosx=(sqrt2)/4# for #0^@<=x<=360^@#, and why?

1 Answer
Oct 16, 2015

First and fourth.

Explanation:

You should look for the quadrants in which the cosine is positive. Since the cosine is the #x#-projection of the points in the unit circle, you must look for the quadrants which points have positive #x#-coordinates, and they are the first and the fourth (visually, the top right and bottom right ones).