14? With sine theorem? A+ group 2b=2c

COSC = (A 2+B 2-C 2)/2AB? C is replaced by a+ group 2b=2c.

Get a formula? Use? Average inequality? You can get the answer. (Square root of 6-2) /4

Reading 20 questions.

The third question is my analysis:

Any given arithmetic series AB has a solution.