If the middle line of an edge of a triangle is equal to half of the edge, then the triangle is a right triangle

I can't draw a picture. Just draw a triangle ABC, D is the middle point of BC, then the middle line ad = BD = CD
Because ad = BD = CD, in triangle BDA and triangle CDA, angle B = angle bad, angle c = angle CAD (the characteristic of isosceles triangle). In triangle ABC, angle BAC + angle B + angle c = 180 degrees
That is, BAC + CAD + bad = 180 degrees
That is, if the 2 * angle BAC = 180 ° then the angle BAC = 90 °

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