isosceles triangle ABC,
the outer angle at apex A is 130 °,
АС – base,
AB and BC – lateral sides.
Find the degree measures of angle A and angle C -?
1) If the outside angle at the vertex A is 130 °, then
angle ABC = 180 ° – 130 °;
angle ABC = 50 °;
2) consider the triangle ABC. The sum of the degree measures of the angles of any triangle is 180 ° and the angle A = angle C, as the triangle ABC is isosceles. Hence:
angle A + angle B + angle C = 180 °;
angle A + angle C = 180 ° – 50 °;
angle A + angle C = 130 °;
angle A = angle C = 130 ° / 2;
angle A = angle C = 65 °.
Answer: 65 degrees; 65 degrees.
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