Answer:
Triangle ADC is a right triangle.
Explanation:
Triangles Classification
An acute triangle is a triangle with three acute angles or with less than 90° each.
An obtuse triangle has one obtuse angle or more than 90°.
A right triangle has one right angle of 90°
From the figure, we can see angle D is marked as a right angle (90°), thus triangle ADC is a right triangle.
To complete the answer, triangle ADB is obtuse (has an angle of 100°), and triangle ABD is acute.