Step 1: Direct Substitution Always try plugging in the value first. If you get a defined number, that's the answer.
Step 2: Identify the Indeterminate Form If substitution fails, identify which of the 7 forms you have. This determines your technique.
Step 3: Choose Technique Based on Form
For 0/0:
- Polynomial? Factorize.
- Square root present? Rationalize.
- Trig/exponential? Standard limits or Taylor.
- Complex? L'Hopital.
For infinity/infinity:
- Polynomial ratio? Divide by highest power.
- Otherwise? L'Hopital.
For 1^infinity:
- Apply e^(lim g*(f-1)) directly.
For 0 * infinity:
- Convert to 0/0 or inf/inf by flipping one factor.
For infinity - infinity:
- Common factor, rationalize, or combine fractions.
For 0^0 or :
- Take logarithm, evaluate lim g*ln(f), answer is e^(result).
Step 4: Verify Check your answer makes intuitive sense. For example, e^(negative) should be between 0 and 1.
Common Pitfalls:
- Don't use L'Hopital when a simpler method exists
- Don't forget to verify the indeterminate form before each L'Hopital application
- Don't confuse the quotient rule with separate differentiation
- For x -> negative infinity, remember sqrt() = -x