1.2 Co-interior angles are A. Obtuse B. Supplementary C. Complementary D. \( 180^{\circ} \)

Co-interior angles, also known as consecutive interior angles, are formed when a transversal intersects two parallel lines. These angles are always supplementary, which means their measures add up to \( 180^{\circ} \). This particular relationship allows us to solve many geometric problems related to parallel lines and transversals, making it crucial for students to grasp! When dealing with co-interior angles in real-world applications, these concepts are often at play in architectural designs and construction. For instance, knowing that co-interior angles must sum to \( 180^{\circ} \) can help architects ensure that walls and beams meet correctly, maintaining both aesthetic beauty and structural integrity.