Show that a non empty interval (a, b) of R contains an infinite set of rational numbers and an infinite set of irrational numbers.
Hint:
1) Show that neither −2 , nor q−2 with q ∈ Q are rationnal.
2) Show that there exists n ∈ N st. a + −2/n ∈ (a, b) and st. a + 1/n ∈ (a, b).
3) Show that for well chosen p, q ∈ Z, one has p/2n ∈ (a, a + 1/n) and q/2n ∈ (a, a + −2/n).