Let us say we have a kite ABCD
with AB = BC
and
CD = DA
If we draw a diagonal across BD, we have two triangles
triangle BCD
and
triangle BAD
Since
AB = BC
and
CD = DA
and
BD = BD (identity property)
triangle BCD = triangle BAD (by SSS postulate)
By virtue of CPCTC, we can prove that
angle B = angle D and
angle C = angle A
