a

  • yetAnotherUser@feddit.de
    link
    fedilink
    arrow-up
    4
    ·
    1 year ago

    What is ∞ + ∞?

    Let x_n be an infinite, real sequence with lim(n -> ∞) x_n = ∞.

    Let y_n be another infinite, real sequence with lim(n -> ∞) y_n = ∞.

    Let c_n be an infinite sequence, with c_n = 0 for all n ∈ ℕ.

    Since y_n diverges towards infinity, there must exist an n_0 ∈ ℕ such that for all n ≥ n_0 : y_n ≥ c_n. (If it didn’t exist, y_n wouldn’t diverge to infinity since we could find an infinite subsequence of y_n which contains only values less than zero.)

    Therefore:

    lim(n -> ∞) x_n + y_n ≥ lim (n -> ∞) x_n + c_n = lim(n -> ∞) x_n + 0 = ∞