9. a. Prove the following statement: Ifr^{3}is irrational, thenris irrational. (by contrapositive)

b. Disprove the converse of the statement in part (a).

a) let r be rational number

for

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

counterexample??