Remainder Theorem

A powerful tool to find the remainder without performing long division.

Introduction

When we divide a polynomial p(x) by another polynomial g(x), we get a quotient q(x) and a remainder r(x).
p(x) = g(x) × q(x) + r(x)
Degree of r(x) < Degree of g(x).

Statement of Remainder Theorem

If p(x) is any polynomial of degree greater than or equal to 1 and p(x) is divided by the linear polynomial (x - a), then the remainder is p(a).

Example

Find the remainder when p(x) = x⁴ + x³ - 2x² + x + 1 is divided by x - 1.
Here, divisor is x - 1, so a = 1.
Remainder = p(1) = (1)⁴ + (1)³ - 2(1)² + 1 + 1 = 1 + 1 - 2 + 1 + 1 = 2.

Practice Questions

Free Preview - 10 Questions

Test your understanding of the Remainder Theorem.

1 Find the remainder when x² - 2x + 4 is divided by x - 2.
  • A 2
  • B 4
  • C 0
  • D -2
Explanation:
Using Remainder Theorem, p(2) = (2)² - 2(2) + 4 = 4 - 4 + 4 = 4.
2 If p(x) is divided by x + 1, the remainder is:
  • A p(1)
  • B p(-1)
  • C p(0)
  • D -p(1)
Explanation:
Comparing x + 1 with x - a, we get a = -1. So remainder is p(-1).
3 What is the remainder when x³ + 3x² + 3x + 1 is divided by x + 1?
  • A 0
  • B 1
  • C 8
  • D -1
Explanation:
p(-1) = (-1)³ + 3(-1)² + 3(-1) + 1 = -1 + 3 - 3 + 1 = 0.
4 If p(x) = x³ - ax² + 6x - a is divided by x - a, remainder is:
  • A a
  • B 5a
  • C -5a
  • D 0
Explanation:
p(a) = a³ - a(a)² + 6a - a = a³ - a³ + 5a = 5a.
5 The remainder when 4x³ - 12x² + 14x - 3 is divided by 2x - 1 is:
  • A 0
  • B 1/2
  • C 3/2
  • D -3/2
Explanation:
Divisor 2x - 1 = 0 → x = 1/2.
p(1/2) = 4(1/8) - 12(1/4) + 14(1/2) - 3
= 1/2 - 3 + 7 - 3 = 1/2 + 1 = 3/2.
6 When p(x) is divided by x, the remainder is:
  • A p(0)
  • B p(1)
  • C p(x)
  • D 0
Explanation:
Checking x = 0 (since x - 0 = x), the remainder is p(0).
7 Check whether the polynomial p(x) = 4x³ + 4x² - x - 1 is a multiple of 2x + 1.
  • A Yes
  • B No
  • C Only for positive x
  • D None
Explanation:
Zero of 2x + 1 is -1/2.
p(-1/2) = 4(-1/8) + 4(1/4) - (-1/2) - 1
= -1/2 + 1 + 1/2 - 1 = 0.
Since remainder is 0, it is a multiple.
8 If x - 1 divides the polynomial kx² - 3x + k completely, find k.
  • A 3
  • B 3/2
  • C 2/3
  • D -3
Explanation:
Since it divides completely, remainder p(1) = 0.
k(1)² - 3(1) + k = 0
2k - 3 = 0 → k = 3/2.
9 If p(x) = x⁹⁹ + 1 is divided by x + 1, remainder is:
  • A 1
  • B 2
  • C 0
  • D -1
Explanation:
p(-1) = (-1)⁹⁹ + 1 = -1 + 1 = 0.
10 What is the remainder when x⁴ + 1 is divided by x - 1?
  • A 0
  • B 2
  • C 1
  • D -2
Explanation:
p(1) = (1)⁴ + 1 = 1 + 1 = 2.

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