One way it's useful is in the application of phasors in physics. Phasors require you to add up vectors of two different angles, so the cosine angle addition formula can be used if you already know the cosine and sine of the original vector angles.
Since 2/3 is equal to 4/6, so you add 4/6 and 1/6 which equals 5/6 which is how much are <span>chocolate and cinnamon. Your leftover would be 1/6.</span>
