This video tutorial explains how you can use the sum and difference identities in trigonometry to determine the sine, cosine, and tangent values of certain angles using angle values you are familiar with. The unit circle helps us visualize the sine and cosine values at 30, 45, and 60 degrees. The sum and difference formulas allow us to combine these values to find the trig values at different angles (ex. 30 + 45 = 75, 60 - 45 = 15, etc).

This video tutorial introduces the Unit Circle and provides a helpful visualization for determining the values of the trigonometric functions at each of the main angles (30, 45, and 60). By knowing the lengths of just three lines, you can quickly find the value of trig functions in all four quadrants of the cartesian coordinate system.