Continuity and Uniform Continuity · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

One delta for every point

Mathematics · Calculus & Analysis · ages 20-21
Name ______________________   Date ____________
  1. Nadia says x squared is continuous at 1 because whenever a sequence converging to 1 is squared, the outputs converge to 1. Is her use of the sequential criterion correct?

    Circle one:   True   False

  2. Which function is continuous but not uniformly continuous on its domain?

    • f(x) equal to x on [0, 1]
    • f(x) equal to 1 over x on (0, 1)
    • The constant function f(x) equal to 5
  3. For f(x) equal to 3x at 2, which delta answers a given epsilon?

    • Delta equal to epsilon over 3
    • Delta equal to epsilon
    • Delta equal to 3
  4. Nadia says x squared is continuous at 1 because whenever a sequence xn converges to 1, xn squared converges to 1. Is her use of the sequential criterion correct?

    Circle one:   True   False

  5. Which function is continuous but not uniformly continuous (on its given domain)?

    • f(x) = 1/x on (0, 1)
    • f(x) = x on [0, 1]
    • The constant function f(x) = 5
    • f(x) = x squared on [0, 1]
  6. The function f(x) equal to x on (0, 1) attains both a maximum and a minimum.

    Circle one:   True   False

  7. Which example shows the closedness hypothesis in the extreme value theorem cannot be dropped?

    • f(x) = x on the open interval (0, 1), which attains neither maximum nor minimum
    • f(x) = x on [0, 1]
    • f(x) = x squared on [0, 1]
    • A constant function on (0, 1)
  8. For f(x) = 3x at c = 2, which delta works for a given epsilon in the epsilon-delta definition?

    • delta = epsilon / 3
    • delta = epsilon
    • delta = 3
    • delta = epsilon squared
  9. A student argues 1 over x on (0, 1) must be uniformly continuous because it is continuous at each point. Where is the flaw?

    • Continuity at each point allows a fresh delta per point, while uniformity needs one shared delta
    • 1 over x is actually discontinuous on (0, 1)
    • Uniformity only concerns unbounded functions
  10. Why is f(x) = 1/x not uniformly continuous on (0, 1)?

    • Points near 0 need ever smaller deltas, so no one delta works everywhere
    • It is discontinuous at some point of (0, 1)
    • An unbounded function cannot be continuous
    • Uniform continuity only applies to polynomials
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Answer key

For grown-ups. Fold this page away before handing over the rest.

One delta for every point W1-mt_plWc9raOwz-s1

  1. True · That is exactly the sequential reading of continuity at a point.
  2. f(x) equal to 1 over x on (0, 1) · 1 over x steepens without bound near zero, defeating every shared delta.
  3. Delta equal to epsilon over 3 · Outputs move three times as fast as inputs, so the distance must be cut by 3.
  4. True · That is exactly the sequential criterion applied at the point 1.
  5. f(x) = 1/x on (0, 1) · 1/x is continuous at each point of (0, 1) but explodes near 0, so no single delta works across the domain.
  6. False · Openness drops the closedness hypothesis, and neither bound is attained.
  7. f(x) = x on the open interval (0, 1), which attains neither maximum nor minimum · f(x) = x on (0, 1) is continuous and bounded, but the values 0 and 1 are never attained since the endpoints are missing.
  8. delta = epsilon / 3 · |3x - 6| = 3|x - 2|, so |x - 2| < epsilon/3 forces |f(x) - f(2)| < epsilon.
  9. Continuity at each point allows a fresh delta per point, while uniformity needs one shared delta · Pointwise deltas may shrink toward zero with no positive shared floor.
  10. Points near 0 need ever smaller deltas, so no one delta works everywhere · Continuity holds pointwise, but the needed delta collapses near 0.
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