How to solve it : tan 490 degrees as a function of an angle less than 45 degrees is:
a) tan 40 degrees,
b) - tan 40 degrees
c) cot 40 degrees
d) - cot 40 degrees

Question

How to solve it : tan 490 degrees as a function of an angle less than 45 degrees is: 
a) tan 40 degrees, 
b) - tan 40 degrees 
c) cot 40 degrees 
d) - cot 40 degrees

ranga · Answer

You can subtract a full 360 degrees out of it without affecting any trigonometric function.
tan(490) = tan(490-360) = tan(130)
Since all the choices involve 40 degrees, we need to write it as:
tan(130) = tan(90 + 40) = - cot(40)