Reference angles
Trigonometry comes from two Greek words that translate to triangle and measure.Trigonometry basically tackles all about measuring a triangle, most especially the right triangles. If you remember our discussion previously about Pythagorean Theorem, then you would have fully grasped the core of trigonometry.
Pythagorean Theorem is summarized by the equation $a^2 + b^2 = c^2$, where a and b are both sides of the right triangle, and c is the hypotenuse (or the longest side of the right triangle). From our previous discussion chapter, we know that Trigonometry utilizes the six trigonometric functions. To remember them, we use the mnemonic SOHCAHTOA which stands for sineoppositehypotenuse, cosineadjacenthypotenuse and tangentoppositeadjacent. We will also look at the ASTC way to solve Trigonometric ratios.
Also we will be tackling the angles involved in trigonometry like standard angle, coterminal angles and the reference angles. Standard angles are basically angles formed by a ray and the x axis. The x axis is the initial arm and the other ray would be the terminal arm. The angle formed from the initial side to the terminal side is the standard angle. Coterminal angles on one hand are angles that have the same initial and terminal sides. One of the angles would have a positive measurement while the other would have negative measurement. The other angle is the reference angle and this is the angle formed by the terminal side of another angle and the x axis. We will also have a brief look at the special angles of Trigonometry like the 454590 angles, the 306090 angles, and the 606060 angles.
This chapter would also discuss all about the unit circle. In this chapter we will learn that unit circles are basically just circles in the quadrant and have a radius that has a measure of 1 unit. We can be able to investigate unit circles with graphing calculators to understand them more. We will get to apply this concept as well as the other concepts we have here with some mathematical problems.
Reference angles
Basic concepts:
 Angle in standard position
 Coterminal angles
Lessons

1.
Reference Angle: the acute angle between the terminal arm and the
xaxis, reference angle is always positive$.$
Determine the reference angle: