The things which coincide with one another are:

• (a) Equal to each other
• (b) Unequal
• (c) Double of same thing
• (d) Triple of same thing

When we talk about things that coincide with one another, we're referring to objects or concepts that occupy the same space or have the same value in a certain context. In this case, the correct answer to your question is (a) Equal to each other. Let’s break this down further to clarify why this is the case.

Understanding Coincidence

Coincidence in mathematics and geometry typically means that two or more entities are in the same position or have the same value. For example, if we have two points on a graph that are at the coordinates (2, 3), they coincide because they are exactly the same point.

Exploring the Options

• Equal to each other: This is the correct choice. When two things are equal, they coincide in value or position. For instance, if two angles measure 45 degrees, they coincide because they are equal.
• Unequal: This option does not fit because if two things are unequal, they cannot coincide. For example, if one angle measures 30 degrees and another measures 45 degrees, they do not coincide.
• Double of the same thing: While one thing can be double another, they are not the same and therefore do not coincide. For instance, if one angle is 30 degrees and another is 60 degrees (which is double), they are still distinct.
• Triple of the same thing: Similar to the previous point, if one angle is 30 degrees and another is 90 degrees (which is triple), they are also different and do not coincide.

Real-World Analogy

Think of it like two people standing in the same spot on a stage. If both are at the exact same coordinates, they coincide. However, if one person moves to a different location, they no longer coincide. This illustrates how equality in position or value is essential for coincidence.

Conclusion

In summary, when we refer to things that coincide, we are specifically talking about those that are equal to each other. This concept is foundational in various fields, including mathematics, physics, and even philosophy, where understanding the nature of equality and coincidence can lead to deeper insights.