if 90< x < 180 and sinx is 19/28, what is cosx? I though of making a right triangle and doing Pythagorean theorem but I realized it wasn’t a right triangle, what do I do?
Divide 19 by 28 then do inverse sine. I got 42.7 degrees.
Sketch it in the unit circle.
Note that the angle 180 - 42.7 degrees would hit the unit circle at the same y coordinate.
See in this illustration how sine(30) = sine(180-30), same idea
http://www.coolmath.com/precalculus-review-calculus-intro/precalculus-trigonometry/28-the-unit-circle-01
Sigh, I used to know how to do all those problems! It’s been too many years now.