- Where it is undefined
- Factor, then cancel
- Factors cancel, terms do not
- Multiply: factor, cancel, multiply
- Divide: flip the second
- Excluded values and closure
- Same denominator
- The least common denominator
- Unlike denominators
- Complex fractions and parallel resistors
- Writing it by inspection
- Writing it by long division
- What it does for large x
- Unlocks after
- Opens up