To prove that the sum \( t = r + s \) is irrational if \( r \) is rational and \( s \) is also rational, the correct sequence of steps would be:
Step 2: For a contradiction, assume that \( t \) is rational, and write \( r \) and \( t \) as fractions.
Step 4: Find a common denominator.
Step 1: Subtract, writing \( s \) as a fraction.
Step 3: Realize a contradiction.
So, the correct sequence is:
Step 2, Step 4, Step 1, Step 3.