Limits

Find the value a function approaches as x tends to a number or to infinity, using direct substitution first, factorising and cancelling when substitution gives the indeterminate form 0/0, and comparing leading terms when x tends to infinity.

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Te reo Māori terms

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Learning objective overview

Master Teaching Guide coverage for this objective.

Resources

  • Other: Not in Beta Textbook; no verified external resource found (this NCEA Level 3 calculus content -- evaluating limits by direct substitution, factor-cancel on 0/0 forms, and comparing leading terms as x tends to infinity -- is not covered by CorbettMaths, Dr Austin Maths, Maths Genie, or Physics & Maths Tutor, none of which teach limits as a standalone GCSE/pre-calculus topic; consistent with sibling LO lo-gradient-of-tangents-on-curves' own prior 'no good match found' note)

Terminology

  • limit
  • tends to
  • approaches
  • direct substitution
  • factorise
  • common factor
  • indeterminate form
  • difference quotient
  • infinity
  • leading term
  • limit does not exist
  • gradient of tangent

Task goals

  • Evaluate the limit of a polynomial as x tends to a given value by substituting the value directly into the expression.
  • Recognise that direct substitution producing 0/0 is an indeterminate form, and factorise the numerator so the common factor cancels with the denominator before substituting again.
  • Evaluate the limit of a simple rational function as x tends to infinity, using the fact that a constant over a power of x tends to 0 and comparing the leading terms of the numerator and denominator.
  • Apply factor-and-cancel to rational functions where both the numerator and the denominator factorise, including difference-of-squares, difference-of-cubes, and repeated-factor cases.
  • Simplify and evaluate a difference-quotient limit as h tends to 0 for a quadratic expression by expanding the bracket, cancelling the common factor of h, then letting h tend to 0.
  • Apply the same difference-quotient process to cubic and quartic expressions, including ones written in other variables such as a and b, and to a function given in the form [f(x + h) - f(x)]/h.
  • Explain what it means for a limit to exist at a point x = a, and give an example of a function whose limit does not exist there.
  • Find an unknown constant in a rational expression given the value of its limit, and set out a step-by-step argument showing that the limit of [(x + h)^n - x^n]/h as h tends to 0 equals n times x^(n-1) for a given value of n.

Key skills

  • Evaluate limit by direct substitution
  • Recognise indeterminate form
  • Factorise and cancel to evaluate a limit
  • Evaluate limit as x tends to infinity
  • Compare leading terms of numerator and denominator
  • Evaluate a difference quotient limit
  • Explain whether a limit exists

Quick stats

  • 81 total questions
  • 3 difficulty levels
  • Answers included