6. Knowing the set of real numbers is not denumerable, prove the set of irrational numbers is not denumerable. 7. a) How many passwords use the digits 3,4,5,6,7,8 and 9 each exactly once? b) How many of those passwords begin and end with an even digit? 8. a) Calculate (a + x). b) Calculate (3x-2y). 6. Knowing the set of real numbers is not denumerable, prove the set of irrational numbers is not denumerable. 7. a) How many passwords use the digits 3,4,5,6,7,8 and 9 each exactly once? b) How many of those passwords begin and end with an even digit? 8. a) Calculate (a + x). b) Calculate (3x-2y).