If 0 lies in the quadrant IV. What can be the value of cos 0 ?
The angle 0 does not lie in any of the four quadrants, it lands directly in between quadrants I and IV. The value of cos 0 is always 1.
In fact, if you are worried that the value might be a negative, it will not, because cos n is always positive if n is in quadrants I or IV, so either way, cos 0 will be positive 1.