Question

find $m\angle abd$.
image of angle diagram with right angles and 20° angle
$m\angle abd = \boxed{1}^\circ$

Explanation:

Step1: Identify Angle Bisector

BD is the angle bisector (since \( DC \perp BC \) and \( DA \perp AB \), and \( DC = DA \) (marked congruent), so by Angle - Bisector Theorem, \( \angle ABD=\angle CBD \)).

Step2: Determine \( m\angle ABD \)

Given \( m\angle CBD = 20^{\circ} \), so \( m\angle ABD=m\angle CBD = 20^{\circ} \).

Answer:

\( 20 \)