1：How to use Sine(two sides are known) and Cosine formula(three sides are known)
2: Arithmetic sequence was about common difference, while geometric was about common ratio
3: When being asked for angle, we need to press shift on the calculator first
4: When we simplify the radical, we need to find the greatest common denominator
5: When solving the equation, we need to check carefully and plug the answers into the primary formula because some of the answers does not fit the formula.