Question

the angle A of the triangle ABC, in which (a+b+c)(b+c-a)= 3bc is

Answer 1

[( b+c ) + a][ ( b+c ) - a] = b² + c² + 2bc -a² => (b² + c² - a²) = bc
=>(b² + c² - a²) = 2bc/2
=>(b² + c² - a²)/2bc = 1/2
=>Cos A = 1/2
=> A = 60°

Answer 2

Answer:

hope it helps you friend