# Chapter 1 - Tools of Geometry - Chapter Review - Page 73: 20

$\angle ADB\text{ and }\angle BDC\text{ are complementary.}$

#### Work Step by Step

$\text{Complementary}$ angles are two angles whose sum is $90^{\circ}$. Since $\angle ADB\text{ and }\angle BDC$ are adjacent and form a right angle, they fit this definition, and we can consider them to be $\text{complementary}$.

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