Question

A triangle has two equal sides.

a)
What is the special name for this type of triangle?
b)
One of the angles in this triangle measures 100°
What is the size of each of the other two angles?

Answer 1

a) isoceles

b) 40°

Explanation:

a) an isoceles triangle has 2 sides of equal length

b) Two interior angles of an isoceles triangle are equal.

Also, the sum of the interiors angles of any triangle = 180°

We are told that one of the angles measures 100°. This angle cannot be one of the 2 equal angles, as 2 x 100° = 200° which is greater than the sum of all three angles.

Therefore, the sum of the 2 equal angles must be 180 - 100 = 80

Therefore, the size of one of them = 80 ÷ 2 = 40°