Proof Techniques Proof Methods (III): Contradiction and Contrapositive Proof by Contradiction Proof by Contrapositive Proof. (Use proof by contradiction.) Suppose that there exists an n such that Q.1) Negation of the statement is A) nZ,EVEN(n)EVEV(n2) B) nZ, such that EVEN(n2)EVEN(n). Proof Techniques Proof Methods (III): Contradiction and Contrapositive Proof by Contradiction Proof by Contrapositive Proof. We prove the contrapostive: Q.2) Contrapositive of the statement is " A) nZ,EVEN(n)EVEV(n2) B) nZ,EVEN(n)EVEN(n). Proof Techniques Proof Methods (III): Contradicti Proof by Contradiction Proof by Contrapositive Proof Techniques Proving If-and-Only-If Statements Proof. ("If" Part) We show that if both x and y are odd, then xy is odd. Q.4) What method/strategy would you use? A) Generalizing from Generic Particular B) Proof by Cases C) Proof by Contrapositive