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Remainder Theorem




 
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In this lesson, we will look into the Remainder Theorem.

What is the Remainder Theorem?

Recall that for long division for integers, the dividing process stops when the remainder is less than the divisor.

dividend = divisor × quotient + remainder

The process is similar for division of polynomials. The dividing stops when the remainder is less that the degree of the divisor.

The Remainder Theorem states that

If a polynomial f(x) is divided by a linear divisor (xa), the remainder is f(a)

Hence, when the divisor is linear, the remainder can be found by using the Remainder Theorem.

How to use the Remainder Theorem?

Example:

Find the remainder when 4x3 – 5x + 1 is divided by

a) x – 2
b) x + 3
c) 2x – 1

Solution:

Let f(x) = 4x3– 5x + 1

a) When f(x) is divided by x – 2, remainder,

R = f(2) = 4(2)3– 5(2) + 1 = 23

b) When f(x) is divided by x + 3, remainder,

R = f(–3) = 4(–3)3– 5(–3) + 1 = –92

c) When f(x) is divided by 2x – 1, remainder,

Example:

The expression 4x2px + 7 leaves a remainder of –2 when divided by x – 3. Find the value of p.

Solution:

Let f(x) = 4x2px + 7

By the Remainder Theorem,

f(3) = –2

4(3)2– 3p + 7 = –2

p = 15




How to use the Remainder Theorem to find the remainder?
Examples:
Use the Remainder Theorem to find the remainder
1. (3x3 - 2x2 + x - 6) ÷ (x - 4)
2. (-4x3 + 8x2 + 12x + 16) ÷ (x + 2)
3. (x6 + 4x5 + 9x3 - 4x2 + 10) ÷ (x + 1) How to find the remainder in a polynomial division?
Examples:
Find the remainder using the Remainder Theorem
(4x4 + 2x2 + 1) ÷ (x - 3)


 
How to use the remainder and factor theorem in finding the remainders of polynomial divisions and also the factors of polynomial divisions?

The Remainder Theorem states that if a polynomial f(x) is divided by (x - k) then the remainder r = f(k). It can assist in factoring more complex polynomial expressions.
The Factor Theorem states that a polynomial f(x) has a factor (x - k) if and only f(k) = 0. It is a special case of the Remainder Theorem where the remainder = 0. How to use the Remainder Theorem to test the factor of a polynomial?
Example:
Is x - 3 a factor of 24 - 11x3 + 15x2 + 4x - 12?

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