Proof positive law of cosines

Foreword

Sine prove

A ideas: the use of high proof triangular sine theorem;

Thinking 2: Using the law of sines proof area of ​​a triangle;

Thinking three: Vector prove the law of sines

Ideas Four: proof circumscribed circle of triangle

Ideas Five: prove with the law of cosines law of sines

To be added

Proof of the law of cosines