NCERT Solution Class IX Mathematics Triangles Question 8 (Ex 7.2)

Question 8:

Show that the angles of an equilateral triangle are 60º each.

Answer:

 

Let us consider that ABC is an equilateral triangle.

Therefore, AB = BC = AC

AB = AC

∠C = ∠B (Angles opposite to equal sides of a triangle are equal)

Also,

AC = BC

∠B = ∠A (Angles opposite to equal sides of a triangle are equal)

Therefore, we obtain

∠A = ∠B = ∠C

In ∆ABC,

∠A + ∠B + ∠C = 180°

∠A + ∠A + ∠A = 180°

3∠A = 180°

∠A = 60°

∠A = ∠B = ∠C = 60°

Hence, in an equilateral triangle, all interior angles are of measure 60º.

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