# In an isosceles triangle ABC with base BC B = 40 degrees. Find the adjacent corner at vertex C.

September 30, 2021 | education

| Given:

isosceles triangle ABC,

ВС – base,

angle B = 40 degrees.

Find the degree measure of the adjacent angle at the vertex C -?

Solution:

Consider an isosceles triangle ABC. In it, the angles at the base are equal, that is, the angle B = angle C = 40 degrees. Knowing that the sum of the degree measures of the angles of a triangle is 180 degrees. We get:

angle A = 180 – 40 – 40;

angle A = 100 degrees.

The outer angle of a triangle is equal to the sum of the angles of the triangle that are not adjacent to it. Then the adjacent angle at the vertex C is equal to:

100 + 40 = 140 degrees.

Answer: 140 degrees.

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