Geometry

Question Analysis:  
This is a logic-focused question applying proof by contrapositive.  
The main focus is on reversing and negating the original conditional statement.

Key Concept Explanation:  
For a statement “If p, then q”, its contrapositive is “If not q, then not p”.
Contrapositive is logically equivalent to the original.

Step-by-Step Solution:  
Original: If is irrational, then is irrational.  
Contrapositive: If is rational, then is rational.  
If we can prove the contrapositive, the original statement must be true.