Isosceles Triangle Median: Proving BAD = DAC Angle Equality

Question

Triangle ABC is isosceles (AB=AC).

AD is the median.

Is it true that BAD=DAC ∢\text{BAD}=∢\text{DAC} ?

AAABBBCCCDDD

Video Solution

Solution Steps

00:00 Determine whether the angle BAD is equal to the angle DAC
00:03 The following is an isosceles triangle
00:09 AD is a median according to the given information, a median intersects the side
00:12 In an isosceles triangle, the median is also the height
00:20 The height creates a right angle with the side it meets
00:25 In an isosceles triangle, the median is also an angle bisector
00:34 This is the solution

Step-by-Step Solution

To solve this problem, we need to examine the properties of an isosceles triangle where the median is drawn from the vertex to the base.

Given ABC \triangle ABC is isosceles with AB=AC AB = AC , and AD AD is the median to the base BC BC , it follows certain properties specific to isosceles triangles:

  • In an isosceles triangle, the median from the vertex angle is also the altitude and the angle bisector for the angle at the vertex.
  • Since AD AD is the median, BD=DC BD = DC .
  • This particular property of isosceles triangles means that AD AD not only divides the base BC BC equally but also divides the vertex angle BAC\angle BAC equally, thus forming the angle bisector.

Therefore, the angle BAD\angle BAD is equal to DAC\angle DAC because AD AD serves as the angle bisector of BAC\angle BAC in the isosceles triangle ABC \triangle ABC .

Thus, it is true that BAD=DAC \angle BAD = \angle DAC in this triangle.

Yes.

Answer

Yes.