Determine the angles of an isosceles triangle ARM if the outer angle of the apex angle R is 129 °.
August 27, 2021 | education|
We are given an isosceles triangle ARM, and we also know that the outer angle at the vertex R is 129 °.
In order to find the remaining angles, we apply the properties of the angles of an isosceles triangle and the theorem on the sum of the angles of a triangle.
Find the inner corner of the triangle adjacent to the outer corner. The sum of adjacent angles is 180 °.
180 ° – 129 ° = 51 °.
If this is an angle at the base, then two angles are 51 ° each and an angle at the apex of 180 ° is 2 * 51 ° = 78 °.
51 ° – apex angle.
(180 ° – 51 °) / 2 = 129 ° / 2 = 64.5 ° angles at the base.
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