Question

write each of the following as trigonometric ratios of acute angles.
(a)sin160 degrees
(b)cos 310 degrees
(c)tan 200 degrees

Answer 1

I do these in 2 steps
1. in which quadrant is the angle, this determines the + or 1
2. How far is the angle from the x-axis, this gives me the "angle in standard position" , always an acute angle

so for b)
1. 310° is in IV, and in IV the cosine is positive. So cos 310 is positive.
2. 310 is 50° to the x-axis

so sin 310° = sin 50°

do the others the same way, and check results with a calculator.