Reference Angles and Triangles
Problem: The value of Sin 390° is equal to?
Solution The value of Sin 390° is equal to
Solution The angle is one complete revolution plus 30º.
Solution Look at the triangle, it can be seen that Sin 390º = and that Cos 60º
Step 3: (in the same triangle) is that same result.
Solution Answer: Sin 390° = Cos 60°
Try two practice problems: