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?
Video Solution
Solution Steps
00:00Determine whether the angle BAD is equal to the angle DAC
00:03The following is an isosceles triangle
00:09AD is a median according to the given information, a median intersects the side
00:12In an isosceles triangle, the median is also the height
00:20The height creates a right angle with the side it meets
00:25In an isosceles triangle, the median is also an angle bisector
00:34This 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 is isosceles with AB=AC, and AD is the median to the base 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 is the median, BD=DC.
This particular property of isosceles triangles means that AD not only divides the base BC equally but also divides the vertex angle ∠BAC equally, thus forming the angle bisector.
Therefore, the angle ∠BAD is equal to ∠DAC because AD serves as the angle bisector of ∠BAC in the isosceles triangle △ABC.