Proof: Because the angle BDA== 1 10, the angle B=40 degrees.

So the angle BAD=30 degrees

Because AB=AC and angle B=40 degrees.

So the angle BAC= 100 degrees.

So the angle DAE=70 degrees

In the triangle ADE, because the angle DAE=70 degrees, the angle ADE=40 degrees.

AED angle =70 degrees.

So AD=ED

So triangle ADE is an isosceles triangle.