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Remainder Theorem: Definition and Examples | EDU.COM

Remainder Theorem: Definition and Examples | EDU.COMEDU.COMResourcesBlogGuidePodcastPlanBackHomesvg]:size-3.5">Math Glossarysvg]:size-3.5">Remainder TheoremRemainder Theorem: Definition and ExamplesTable of ContentsRemainder Theorem Definition of Remainder Theorem

The remainder theorem provides a shortcut for finding remainders when dividing polynomials. When we divide a polynomial p(xxx) by (x−a)(x − a)(x−a), the remainder equals p(aaa) - the value of the polynomial when x=ax = ax=a. So instead of doing long division, we can simply substitute x=ax = ax=a into the original polynomial to find the remainder.

The degree of the remainder polynomial is always 1 less than the degree of the divisor polynomial. When any polynomial is divided by a linear polynomial (polynomial with degree = 1), the remainder is always constant (degree = 0). Additionally, (x−a)(x − a)(x−a) is a divisor of the polynomial P(xxx) if and only if P(aaa) = 0, which is why this theorem is also used to factorize polynomials.

Examples of Remainder Theorem Example 1: Finding Remainder Using the Theorem Problem:

Find the remainder when p(x)=x2+4x+4p(x) = x^2 + 4x + 4p(x)=x2+4x+4 is divided by (x−1)(x − 1)(x−1).

Step-by-step solution:

Step 1, Find the value of aaa by setting the linear polynomial equal to zero.

x−1=0⇒x=1x - 1 = 0 \Rightarrow x = 1x−1=0⇒x=1 So, a=1a = 1a=1

Step 2, Use the remainder theorem formula. The remainder equals p(a)p(a)p(a).

Remainder = p(1)p(1)p(1)

Step 3, Substitute the value of aaa into the polynomial.

p(1)=12+4(1)+4p(1) = 1^2 + 4(1) + 4p(1)=12+4(1)+4

Step 4, Solve the expression.

p(1)=1+4+4=9p(1) = 1 + 4 + 4 = 9p(1)=1+4+4=9

Step 5, The remainder is 999.

Example 2: Finding Remainder with a Different Linear Divisor Problem:

Find the remainder when f(x)=2x2+4x−4f(x) = 2x^2 + 4x − 4f(x)=2x2+4x−4 is divided by (2x−1)(2x − 1)(2x−1).

Step-by-step solution:

Step 1, For the divisor (2x−1)(2x - 1)(2x−1), we need to find where it equals zero. 2x−1=0⇒x=122x - 1 = 0 \Rightarrow x = \frac{1}{2}2x−1=0⇒x=21​. Note: To apply the remainder theorem directly, we could also rewrite (2x−1)(2x - 1)(2x−1) as 2(x−12)2(x - \frac{1}{2})2(x−21​).

Step 2, Use the remainder theorem. The remainder equals f(a)f(a)f(a).

Remainder = f(12)f(\frac{1}{2})f(21​)

Step 3, Substitute x=12x = \frac{1}{2}x=21​ into the polynomial.

f(12)=2(12)2+4(12)−4f(\frac{1}{2}) = 2(\frac{1}{2})^2 + 4(\frac{1}{2}) - 4f(21​)=2(21​)2+4(21​)−4

Step 4, Simplify each term.

f(12)=2(14)+4(12)−4f(\frac{1}{2}) = 2(\frac{1}{4}) + 4(\frac{1}{2}) - 4f(21​)=2(41​)+4(21​)−4 f(12)=12+2−4f(\frac{1}{2}) = \frac{1}{2} + 2 - 4f(21​)=21​+2−4

Step 5, Calculate the final result.

f(12)=−32f(\frac{1}{2}) = \frac{-3}{2}f(21​)=2−3​

Step 6, The remainder is −32\frac{-3}{2}2−3​.

Example 3: Checking if a Binomial is a Factor of a Polynomial Problem:

Check if (x+3)(x + 3)(x+3) is a factor of x2+6x+9x^2 + 6x + 9x2+6x+9.

Step-by-step solution:

Step 1, Rewrite (x+3)(x + 3)(x+3) as (x−(−3))(x - (-3))(x−(−3)) to match the form (x−a)(x - a)(x−a).

So, a=−3a = -3a=−3

Step 2, According to the remainder theorem, (x−a)(x - a)(x−a) is a factor of a polynomial p(x)p(x)p(x) if and only if p(a)=0p(a) = 0p(a)=0.

Step 3, Calculate p(−3)p(-3)p(−3) by substituting x=−3x = -3x=−3 into the polynomial.

p(−3)=(−3)2+6(−3)+9p(-3) = (-3)^2 + 6(-3) + 9p(−3)=(−3)2+6(−3)+9

Step 4, Simplify the expression.

p(−3)=9−18+9=0p(-3) = 9 - 18 + 9 = 0p(−3)=9−18+9=0

Step 5, Since p(−3)=0p(-3) = 0p(−3)=0, we can say that (x+3)(x + 3)(x+3) is indeed a factor of x2+6x+9x^2 + 6x + 9x2+6x+9.

Comments(4)TTableTennisPlayerTheoNovember 6, 2025I've been struggling to explain the remainder theorem to my students. This page's clear def and examples made it so much easier! Thanks!

DDesignerMonaNovember 5, 2025I've used this remainder theorem def for my students. It's super clear! The examples really helped them grasp the concept fast.

WWebDeveloperXenaNovember 5, 2025This glossary page on the remainder theorem is great! It helped my students grasp the concept easily. Thanks for the clear def and examples!

MCMs. CarterSeptember 17, 2025This explanation of the Remainder Theorem was so clear! I used the examples to help my son with his algebra homework, and he finally got it. Thanks for the step-by-step breakdown—it’s a lifesaver for parents!

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