Question 172860
AD is congruent to DC because BD bisects AC
BD is a shared side of triangles BDA and BDC
angles ADB and CDB are both right angles and so are congruent
Triangles ADB and CDB are congruent by SAS
Angles CBD and ABD are congruent because these triangles are congruent
Angles CBD and BCD are conplementary because they are the acute angles in a right triangle
Angle ABD is then complementary to BCD because ABD and CBD are congruent