What is angle DAB?

Question

There are two triangles: ABC and BDC. Angle A in triangle ABC is 40 degrees. Angle C in triangle ABC is 20 degrees. Line AD = BC. What is angle D in triangle ABD?

Answer 1

Hi Darshil,

First of all very clean and accurate you draw two triangles .

You will have a 4 sides ( quadrilateral) that angle A of ABC and angle D of ΔBDC are two opposite angles of

quadrilateral that sum of them is 180

A = 40 ------> 180 - 40 = 140 = < D of Δ BDC

I hope it is useful,

Minoo

Answer 2

angle ABC is 120

but There is not enough evidence to show the triangles are the same...

AD = BC is given and BD = DB by reflexive

Let angle ABD is x

then angle CBD is 120-x

angle BDA = 140-x

angle BDC = x+40

since BD is NOT perpendicular, there are no other equal sides