Question

(a + b+c) (a+b-c) = 3bc, prove that angel c= 60°
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Answer 1

In a Triangle ABC,

If (a + b + c) (a + b - c) = 3ab, then Angle C = 60°

To prove :

⇒(a + b + c) (a + b - c) = 3ab

⇒(a + b)² - c² = 3ab

⇒ a² + b² - c² + 2ab = 3ab

⇒a² + b² - c² = 3ab - 2ab

⇒ a² + b² - c² = ab

⇒ a² + b² - c²/ 2ab = 1/2

⇒ cosC = 1/2

⇒ cos C = cos 60°

⇒ ∠C = 60°

Therefore, The angle C is 60°

Answer 2

Step-by-step explanation:

the the answer is cosine 60 degree