4. [Disproof by Counter Example] Prove that the following statements are false. a) x²=4 => x=2. b) For all real values of a and b, a-b>0 a²-b² >0. c) The sum of two unequal, positive, irrational numbers is irrational. d) The product of two unequal, positive, irrational numbers is irrational.

I need help.

Let a and b be integers, and let d be a positive common multiple of a and b. Show that the following two statements are equivalent.  (1) d <= c for every positive common multiple c of a and b. (2) d divides c for every common multiple c of a and b.

X || 6 [145]++84)]-[83] X 6 -7 = -6