Determine the angles of an isosceles triangle DRP if the outer angle of the angle D at the base DP is 161 °.

If angle D is opposite to the base of the triangle.

The outer angle of a triangle is equal to the sum of two non-adjacent inner angles, then DPR + DRP = ADR = 161.

Since the triangle is isosceles, then the angle DRP = DPR, then DRP = DPR = 161/2 = 80.5.

The PDR angle is adjacent to the ADR angle, then the PDR angle = 180 – 161 = 19.

Answer: The angles of the triangle are 19, 80.5, 80.5.



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