The vertical angle of an isosceles triangle is 100°. Find its base angles.

Given: The given triangle is isosceles triangle. Also vertex angle is 100°


To find: Measure of base angles.


It is given that triangle is isosceles.


So let our given triangle be ∆ABC.


And let A be the vertex angle, which is given as A= 100°


By the property of isosceles triangle, we know that base angles are equal.


So,


B = C …(1)


We know that,


Sum of all angles in any triangle = 180°


A + B + C = 180°


100° + 2B = 180° …from (1)


2B = 180° - 100°


2B = 80°


∴∠B = 40°


Therefore, our base angles, B and C, are 40° each.


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