I have two questions in my packet that I'm not completely show how to do. Any help is appreciated.

Q1) prove that the sum of square root of 2 and square root of 3 is irrational. [hint: prove square root of six is irrational and then use this as a lemma]

Q2) Suppose a,b,c,d is a set of integers such that a/c and b/c. Show that ab/cd.