Keep the operation and the original domain
Algebraic fractions follow the usual fraction rules. Record restrictions before cancelling, then use the requested coefficient convention
- Record restrictions first Every original denominator must be nonzero. When dividing, the divisor must also be nonzero
- Cancel whole factors Factorise where needed. Divide a complete numerator and denominator by the same nonzero factor; do not cancel addends
- Multiply or use a reciprocal Multiply numerators and denominators. For division, reverse only the divisor before multiplying
- Use a common denominator For addition and subtraction, convert both fractions to the same denominator. Subtract the entire second numerator
- Keep the original domain A cancelled factor still excludes its original zero. An equivalent simplified rule is used only at the original allowed inputs
Worked example
Simplify while retaining every original restriction
- \(\displaystyle x^2+3x+2=(x+1)(x+2)\)The original denominator excludes −1 and −2.
- \(\displaystyle x^2-4=(x-2)(x+2)\)Factorise the numerator as a difference of squares
- \(\displaystyle \frac{(x-2)(x+2)}{(x+1)(x+2)}\)Cancel the complete common factor x + 2 only at original allowed inputs
- \(\displaystyle \frac{x-2}{x+1}\)The denominator is monic, so its coefficients are 1 and 1.
- \(\displaystyle x\notin\{-2,-1\}\)Both original exclusions remain, including the cancelled one
Common mistakes
Difficulty levels
Questions about this topic
Why does cancelling a factor not restore an input?+
The original denominator was zero at that input. The simplified rule agrees with the original only on its original domain
What extra restriction appears in division?+
The divisor must be defined and nonzero. Record zeroes of its original denominator and its numerator before reversing it
Why do the tables require a monic denominator?+
Otherwise multiplying numerator and denominator by the same number gives infinitely many coefficient tables for the same fraction. The convention makes the requested entries definite
What does a zero coefficient mean?+
The corresponding power is absent. For example, x² − 4 has x coefficient zero, and x has constant zero
Can I use a calculator?+
No. This topic is practised without a calculator
Which year level and chapter is this?+
Year 11, VCE Units 1 & 2, Mathematical Methods, chapter 2: Algebraic foundations