An isosceles triangle is a triangle in which the sides are equal.
The sum of all the angles of a triangle, regardless of its type, is 180º. Since in an isosceles triangle the angles at the base are equal, then an obtuse angle in it can only be the angle opposite to the base, that is, the angle ∠B.
∠А = ∠С = (180º – ∠В) / 2;
∠А = ∠С = (180º – 140º) / 2 = 40º / 2 = 20º.
The outside angle at the apex of a triangle is the angle adjacent to the apex of the triangle. Together they make up an unfolded angle, the degree measure of which is 180º.
Based on this:
φ = 180º – ∠А
φ = 180º – 20º = 160º.
Answer: The outer angle at the base of this triangle is 160º.
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.