In quadrilateral ACBD, AC=AD and AB bisects ∠A(see Fig). Show that △ABC≅△ABD. What can you say about BC and BD?
InΔABCandΔABD
AC=AD(given)
∠CAB=∠DAB(given)
AC=AB(common)
So, ΔABC≅ΔABD(bySAScriterion)
Now, ΔABC≅ΔABD
⇒BC=BD(byc.p.c.t)
Therefore BC and BD are equal