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Dividing Polynomials: Long & Synthetic Division

When the divisor has more than one term, you need polynomial long division — the same divide-multiply-subtract-bring-down rhythm as long division with numbers.

It looks busy at first, but each round follows the exact same four steps, and the process ends when there is nothing left to bring down.

The four-step cycle

Divide the leading term of the dividend by the leading term of the divisor to get the next quotient term. Multiply that term by the whole divisor and subtract.

Bring down the next term and repeat. Continue until the remaining polynomial has lower degree than the divisor — that leftover is the remainder.

Keep columns aligned

Line up like powers of xx in columns, and insert a zero placeholder for any missing power so nothing shifts.

Subtraction is where sign errors creep in; change the signs of the row you are subtracting and add instead.

Worked examples

Example 1: a clean division

Divide x2+8x+15x+5\dfrac{x^2 + 8x + 15}{x + 5}.

Divide leading termsx2÷x=xx^2 \div x = x
Multiply and subtract(x2+5x)3x+15(x^2 + 5x) \to 3x + 15
Repeat: 3x ÷ x = 3, remainder 0x+3x + 3

Answer: x+3x + 3

Example 2: the stopping rule

When do you stop dividing?

When the leftover degree is smallerdeg(remainder)<deg(divisor)\deg(\text{remainder}) < \deg(\text{divisor})

Answer: When the remainder's degree is below the divisor's

Example 3: a missing power and a nonzero remainder

Divide x34x+1x2\dfrac{x^3 - 4x + 1}{x - 2}.

Insert a zero placeholder for the missing x-squared termx3+0x24x+1x^3 + 0x^2 - 4x + 1
Divide leading termsx3÷x=x2x^3 \div x = x^2
Multiply and subtract(x32x2)2x24x+1(x^3 - 2x^2) \to 2x^2 - 4x + 1
Repeat: 2x-squared ÷ x = 2x, multiply and subtract(2x24x)1(2x^2 - 4x) \to 1
Degree 0 is below the divisor's degree, so 1 is the remainderx2+2x+1x2x^2 + 2x + \dfrac{1}{x - 2}

Answer: x2+2x+1x2x^2 + 2x + \dfrac{1}{x - 2}

Try one yourself

Common questions

What are the four steps?

Divide, multiply, subtract, bring down — then repeat until the remainder has lower degree than the divisor.

What if a power is missing?

Insert a zero placeholder for it (like 0x0x) so the columns stay aligned and no terms shift.

How do I know when to stop?

Stop when the polynomial left over has a lower degree than the divisor. That polynomial is the remainder.

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