Answer:
SSS rule of congruency
Step-by-step explanation:
It is given that ΔABC is isosceles triangle and ΔBDC is also isosceles triangle.
Thus, AB=AC and BD=DC.
Now, consider ΔABD and ΔACD, we have
AB=AC (Because ΔABC is isosceles triangle)
AD=AD(Common side of both triangles)
BD=DC(Because ΔBDC is isosceles triangle)
Therefore, by SSS congruency rule,
ΔABD≅ΔACD
Hence proved.