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  1. ← All courses
  2. Precalculus
  3. Unit 8: Rational Functions

Lesson 2 of 4

Divide polynomials and check remainders

Use long or synthetic division and verify dividend=divisor times quotient+remainder.

Subject to changeOptional future study, outside the current course sequence. This lesson and its homework preview are unassigned and may change.

Lessons and study tools
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Current units

  1. Unit 1: Essential Review
    1. Find a starting point
    2. Evaluate and compare expressions
    3. Read powers and multiply expressions
    4. Solve equations and describe intervals
    5. Essential algebra review
  2. Unit 2: Functions
    1. Read and use function notation
    2. Combine functions in the right order
    3. Keep inputs and outputs allowed
    4. Describe change and graph behavior
    5. Reverse a function safely
    6. Use symmetry to compare inputs
    7. Functions review
  3. Unit 3: Linear Functions
    1. Build a model with constant change
    2. Write and compare line equations
    3. Reverse a linear model
    4. Build and read piecewise rules
    5. Linear functions review
Optional future study · Subject to change

Unassigned previews outside the current course sequence.

  1. Unit 4: Exponential Functions · Optional future study · Subject to change
    1. Simplify with exponent laws
    2. Interpret rational exponents over the reals
    3. Build repeated-factor models
    4. Solve equations with a common base
    5. Read exponential graphs and their limits
    6. Exponentials review
  2. Unit 5: Quadratics · Optional future study · Subject to change
    1. Factoring patterns
    2. Factoring trinomials
    3. Completing the square
    4. Quadratic models
    5. Linear quadratic systems
    6. Quadratics review
  3. Unit 6: Transformations · Optional future study · Subject to change
    1. Shifts and reflections
    2. Stretches and compressions
    3. Move and reshape a function
    4. Transformations review
  4. Unit 7: Polynomials · Optional future study · Subject to change
    1. Polynomial structure
    2. Polynomial behavior
    3. Polynomial graphs
    4. Polynomials review
  5. Unit 8: Rational Functions · Optional future study · Subject to change
    1. Simplify rational functions safely
    2. Current lessonDivide polynomials and check remainders
    3. Combine rational expressions
    4. Solve rational equations and check candidates
    5. Rational expressions and equations review
  6. Unit 9: Trigonometry · Optional future study · Subject to change
    1. Right-triangle models
    2. Radians and circular arcs
    3. The unit circle
    4. Trigonometric identities
    5. Linear trigonometric equations
    6. Trigonometry review
  7. Unit 10: Trigonometric Graphs · Optional future study · Subject to change
    1. Sine and cosine models
    2. Period, frequency, and phase
    3. Build a sine or cosine model
    4. Sine and cosine graphs review
  1. 1Learn it
  2. 2Practice it
  3. 3Homework
  4. 4Finish

Step 1 of 4: Learn it

Learn it · 1 of 8The ideas you will useNext: A problem-solving deskChoose an activity

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Big ideas · 1 of 8

Big ideas

The ideas you will use

Do this: Read one idea, then explain it in your own words.

Key words

  • Key word · Unit 8RemainderWhat is left after polynomial division.Exactly: In P(x)=D(x)Q(x)+R(x), the remainder is zero or has smaller degree than the nonzero divisor D. For division by x−c, the remainder is P(c).Mix-up alert: Use c, not -c, when dividing by x-c in synthetic division.See this in Key words
  • Write powers in order

    Arrange dividend and divisor in descending powers. Include a zero coefficient for a missing power so each subtraction lines up correctly.

  • Repeat divide and subtract

    In polynomial division, divide leading terms, multiply the divisor by that quotient term, then subtract the whole product. Continue until the remainder degree is less than the divisor degree.

  • Use synthetic division carefully

    The standard coefficient shortcut applies to a divisor x−c. Use c, including its sign, and bring down, multiply and add across the coefficients.

  • A remainder gives a check

    The identity is P(x)=D(x)Q(x)+R(x). For division by x−c, the Remainder Theorem gives remainder P(c); if that is zero, x−c is a factor.

Step-through

A problem-solving desk

Do this: Step through the example. Predict the next step before revealing it.

Worked example: a quotient and remainder

1. Given2. Represent3. Solve4. Check

Whole picture, 4 steps

4 steps. Tap a number or Show me how it works.

Worked example: a quotient and remainder

Do this: Cover the next step and try it yourself.

  1. Step 1: Divide x2+4x+7 by x+2.
  2. Step 2: The first quotient term is x. Subtract x(x+2) to leave 2x+7.
  3. Step 3: The next quotient term is 2. Subtract 2(x+2) to leave remainder 3.
  4. Step 4: The quotient is x+2 and remainder is 3.

Check (x+2)(x+2)+3=x2+4x+7.

Worked example: synthetic division

Do this: Cover the next step and try it yourself.

  1. Step 1: Divide x3−5x+4 by x−1.
  2. Step 2: Use c=1 and coefficients 1,0,−5,4; the zero keeps the missing x2 place.
  3. Step 3: Bring down 1; multiply/add to obtain quotient coefficients 1,1,−4 and remainder 0.
  4. Step 4: The quotient is x2+x−4.

Check (x−1)(x2+x−4)=x3−5x+4, and P(1)=0.

Mix-up alert: check the tempting shortcut

Do this: Explain why the tempting shortcut fails.

Wrong idea: dividing by x+3 means using synthetic value 3. Rewrite the divisor as x−(−3), so the value is −3. Check the sign by plugging it into the divisor: −3+3=0.

Tip

Do Now · Easy · Paper reference

Do this: Use paper. State the definition before you calculate.

What does the remainder theorem let you calculate without completing long division? It gives the remainder as P(a) for division by x−a.

Worked example

Guided practice · Medium · Paper reference

Do this: Work on paper and explain each step before checking it.

Divide x2+2x+7 by x−1.

  1. Step 1: The quotient begins with x.
  2. Step 2: The constant is 3.
  3. Step 3: x2+2x+7=(x−1)(x+3)+10.

Watch

Video: Divide polynomials and check remainders

Do this: Watch the public lesson, pause to try a step, then return to your practice.

Watch on YouTubeOpens in a new tab. Keep your work here.

Watch for:

  • Keeping missing powers in place and checking divisor times quotient plus remainder.
  • Pause before a worked step and try it on paper. Compare the reasoning, not just the final answer.
Open on YouTube↗ (opens in a new tab)

From The Organic Chemistry Tutor · Long Division With Polynomials - The Easy Way!

The linked video is free to watch. The creator may offer optional paid resources; they are not needed for this lesson. If YouTube is blocked, use the lesson notes and worked examples here.

Step 2 of 4: Practice it

What is left (7 of 7)

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Activity 1 of 7 · 0 of 7 activities done

Flashcards

Eight ideas to recall

Do this: Say the answer and a reason before you flip.

Card 1 of 8

Divide polynomials and check remainders

0 Know it0 Still learning

Rebuild the starting polynomial.

Deck options
Keyboard help

On the card: Enter or Space flips. Left and Right move. After revealing, 1 marks Still learning and 2 marks Know it. Tab reaches every control.

Question

What identity checks polynomial division?

Answer

Dividend equals divisor times quotient plus remainder.

Question

Why include a zero coefficient for a missing power?

Answer

It keeps coefficient positions aligned during division.

Question

For divisor x−4, what synthetic value is used?

Answer

4.

Question

For divisor x+6, what synthetic value is used?

Answer

−6.

Question

How small must the final remainder degree be?

Answer

Less than the divisor degree, unless the remainder is zero.

Question

What does the Remainder Theorem say for x−c?

Answer

The remainder equals P(c).

Question

What does remainder zero tell you for x−c?

Answer

x−c is a factor of P(x).

Question

Divide x2−4 by x−2.

Answer

Quotient x+2 and remainder 0.

True or false

Test the boundaries

Do this: Choose true or false; explain what would make a false statement correct.

Statement 1 of 4

The coefficient list for x3+2x−1 is 1,0,2,−1.

Self-test

Check the foundations

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6 questions. One at a time.

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Self-test

Apply and explain

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Write it

Explain your reasoning

Do this: Write two or three sentences, then compare with the model.

Step 1 of 3: Write

A student divides x3+2x−5 by x+1 using coefficients 1,2,−5 and synthetic value 1. Explain both setup errors and find the correct remainder.

Start here if it helps: I would first identify...

0 words · Aim for 20 or more. This is a guide, not a limit.

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Write it

Extra practice · Hard

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Step 1 of 3: Write

Find a quadratic with leading coefficient 1 that has remainders 4 and 7 when divided by x−1 and x−2 respectively. Explain uniqueness.

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Match

Match the key words

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Connect the ideas

0 / 4 connected

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Terms

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Step 3 of 4: Homework

Subject to changeOptional preview. This page does not mean this homework is assigned. Only turn it in if your teacher asks.

Optional practice preview · 3 points if assigned

Divide polynomials and check remainders practice preview

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Step 4 of 4: Finish

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Next lesson: Combine rational expressionsUnit 8: Rational Functions
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Published with approval from Mr. Farzin Khan Shifat. Last updated October 31, 2026.