9. a. Prove the following statement: If r3 is irrational, then r is irrational. (by contrapositive)
b. Disprove the converse of the statement in part (a).
a) let r be rational number
by definition integers are closed under multiplication, all integers are rational
therefore r^3 is rational
b) converse is if r is irrational then r^3 is irrational