In an isosceles triangle ABC, the median BM is drawn to its base AC, with ∠МВС = 40⁰. Find ∠ABС.

By the condition of the problem, we have an isosceles triangle ABC.
In this triangle, the median BM is drawn to the base of AC.
The MBC angle is 40 °.
To calculate the value of the angle ABC, remember that in an isosceles triangle, the median drawn to the base is also the bisector.
So it can be written for the ABC angle.
ABC = ABM + MBC.
It is known that ABM = MBC, therefore, for the angle ABC can be written in another way.
ABC = 2 × MBC.
Now let’s substitute the MBC value.
ABC = 2 × 40 °.
ABC = 80 °.
Answer: ABC = 80 °.