Equilateral Triangle

In equilateral triangle,

• All sides are equal
• All angles all equal 60°

In equilateral ∆ ABC,

• AB = AC = BC
• ∠A = ∠B = ∠C = 60°

But, why are all angles 60°?

In equilateral triangle, all angles are equal.

Let ∠A = ∠B = ∠C = x

In ∆ABC

Sum of angles is 180°

  ∠A + ∠B + ∠C = 180°

  x + x + x = 180° 

  3x = 180°         

  x = (180°)/3

  x = 60°

So, ∠A = ∠B = ∠C = 60 °

Thus, all angles are 60°    

For equilateral triangle

Perimeter = 3a

Check proof  

Area = √3/4 a ²

Check proof