Student Video #5: Unit S Concept 4 - Using half-angle formulas

• What is this video about?

This video is about Unit S Concept 4, which explains how to use the half-angle formulas to solve the problem. The given angle does not appear in the Unit Circle and sometimes shows up as a decimal. But we can still solve the 3 trigonometry functions of that half-angle by using half-angle multiply by 2. This video will help review Unit R Concept 1 that is about sum/difference formulas. 

• What does the viewer need to pay special attention to in order to understand the concept?

The readers need to focus when they try to find the quadrant of the angle; in this case, it has to be the half-angle's quadrant. The quadrant is very important because it will give the sine/cosine a positive/negative. Tangent is not really matter about the positive or negative because the numbers will help the readers to figure out.  

• Although the answers look different, they are the same because if we plug them in the calculator, their decimals will be the same. The methods are different but they all solve for the same angle which is 105 degrees. Because 105 does not appear on the Unit Circle, we can use the half-angle formulas or sum/difference formulas to find the answers. The decimal answers that both methods should have are

                                   sin 105 degrees=0.9659258263

                                   cos 105 degrees=-0.2588190451

                                   tan 105 degrees=-3.732050808