Final Answer:
The side bar (AD) is opposite angle ∠ADC in triangle ADC.
Step-by-step explanation:
In triangle ADC, the side opposite an angle is referred to as the "opposite side." In this context, side AD is opposite angle ∠ADC. This naming convention is a fundamental principle in trigonometry, where the relationship between sides and angles in a triangle is crucial for understanding geometric properties.
To elaborate, the angle ∠ADC is formed by sides AD and DC. The side opposite ∠ADC is AD itself. This relationship holds true for any triangle—each angle has a corresponding opposite side. In the case of triangle ADC, if we are considering the angle ∠ADC, side AD is the side directly across from this angle, making it the opposite side.
Understanding these basic principles of triangle geometry and the relationship between sides and angles is essential for various mathematical applications, including solving triangles, calculating trigonometric functions, and analyzing geometric structures. In summary, in triangle ADC, side AD is designated as the side opposite angle ∠ADC, providing a clear and concise way to describe the geometric relationship within the triangle.