ABC is an equilateral triangle. AB = 10 cm, AD bisector. Find the corner BAD.

1) It is known that in an equilateral triangle all sides and angles are equal, and each angle is 60 °.
The bisector of an angle divides it in half.
Therefore, ∠BAD is:
60 °: 2 = 30 °.
2) The bisector AD divides the triangle ABC into two equal right-angled triangles, i.e. ∠BDA is 90 °.
Then, knowing that the sum of the angles of a triangle is always 180 °, we can find ∠BAD by eliminating two known angles:
∠BAD = 180 ° – 60 ° – 90 ° = 30 °.
Answer: ∠BAD is 30 °.