Use only cos rule to prove this = : :
In this case i use cos rule but, after few step i cannot simplify, but i have finish this sum with sine rule, If anyone have a idea to do simplify this sum through cos rule>>>>>>
Use only cos rule to prove this = : :
In this case i use cos rule but, after few step i cannot simplify, but i have finish this sum with sine rule, If anyone have a idea to do simplify this sum through cos rule>>>>>>