The first question, use the double angle formula, right? Because? A-? Sin? A=cos？ A-Kossa

Then move the item to get cosA=?

In a triangle, so A=60 degrees.

The second question, using cosine theorem, a? =b？ +c？ -2bc cosA, and using sine theorem and known conditions, we get b=2c, which brings both A and A into C and B ...

Final area formula S=? bcsinA