Given: triangle ABC, angle ABD = 20 degrees, angle A = 40 degrees BD – bisector Find: angle C.

By definition, the bisector in a triangle divides the angle into two equal parts, then BD divides the angle B in half:

<ABD = <DBA = 20 °.

The sum of all angles in a triangle is 180 °. Find the degree measure of the angle C:

<C = 180 ° – <A – (<ABD + <DBA);

180 ° – 40 ° – (20 ° + 20 °) = 100 °.

Answer: <C = 100 °.



One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.