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How do you identify a jump discontinuity in a piecewise function using one-sided limits?

A jump discontinuity is identified when the left-hand limit and the right-hand limit at a point exist but are not equal. Because the one-sided limits differ, the two-sided limit does not exist, preventing the function from being continuous at that point. For example, if the left limit is 7 and the right limit is 11, the mismatch produces a jump.

Conditions

  • The function is defined on both sides of the point.
  • The left-hand limit and right-hand limit both exist as finite numbers.
  • The left-hand limit does not equal the right-hand limit.

Reasoning, step by step

  1. Calculate the limit as xx approaches the point from the left (x→a−x \to a^-).
  2. Calculate the limit as xx approaches the point from the right (x→a+x \to a^+).
  3. Compare the two values.
  4. If the values are different, conclude that a jump discontinuity exists.
  5. Note that the two-sided limit does not exist.

Example

At x=3x=3 in the first example, the left limit is 7 and the right limit is 11. Their mismatch prevents a two-sided limit and produces a jump.

Common misconceptions

  • Believing that a jump discontinuity means the function is undefined at the point.
  • Confusing a jump discontinuity with a removable discontinuity where limits are equal.
  • Thinking that the function value f(a)f(a) determines the type of jump.

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