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When we prove the statement "All even primes greater than 3 are perfect squares" by observing that there are no even primes greater than 3, we are using which of the following kinds of proofs? Direct proof Trivial proof O Proof by contradiction O Vacuous proof Theorem: The negative of every irrational number is irrational. Proof: 1. Suppose there is some irrational number p such that -p is rational. 2. -p = m, where m and n are both integers and n # 0 3. p= -m, where -m and n are both integers and n # 0 4. p is rational, which is contradiction Which of the following in the proper justification for line 2 in the above proof by contradiction?? Contradictory supposition Algebra Closure of integers under negation Definition of rational numbers