Final answer:
Corresponding angles formed when parallel lines are cut by a transversal are equal, not perpendicular or supplementary.
Step-by-step explanation:
Given parallel lines cut by a transversal, corresponding angles are equal. This is because when two parallel lines are intersected by a transversal, the angles in matching corners (known as corresponding angles) are equal to each other. This can be visualized in terms of vectors as well; two vectors that are parallel will have the same direction, but to be equal, they must also have the same magnitude. However, if two vectors (or lines) are perpendicular, they form a 90° angle between each other, which is not the case for corresponding angles. Therefore, the correct answer is that corresponding angles are (a) equal.