Remainder Theorem

Definition of Remainder Theorem:

Let p(x) be any polynomial of degree greater than or equal to 1 and let α be any real number. If p(x) is divided by the polynomial (x - α), then the remainder is p(α).

In other words:

If the polynomial f(x) is divided by x - α then the remainder R is given by f(x) = (x - α) q(x) + R, where q(x) is the quotient and R is a constant (because the degree of the remainder is less than the degree of the divisor x - α).

Putting x = α, f(α) = (α - α)q(α) + R or f(α) = R

When the polynomial f(x) is divided by x - α, the remainder R = f(α) =  value of f(x) when x is α.

Solved examples on Remainder Theorem:

1. Find the remainder when x$^{3}$ + 3x$^{2}$ + 3x +1 is divided by

(i) x + 1

(ii) x - $\frac{1}{2}$

(iii) x

(iv) x + γ

(v) 5 + 2x

Solution:

(i) Let f(x) = x$^{3}$ + 3x$^{2}$ + 3x +1, divisor is x +1

Then by the Remainder Theorem we get,

Remainder = f(-1)

                  = (-1)$^{3}$ + 3(-1)$^{2}$ + 3(-1) +1

                  = -1 + 3 - 3 + 1

                  = 0

(ii) Let f(x) = x$^{3}$ + 3x$^{2}$ + 3x +1, divisor is x - $\frac{1}{2}$

Then by the Remainder Theorem we get,

Remainder = f($\frac{1}{2}$)

                  = ($\frac{1}{2}$)$^{3}$ + 3($\frac{1}{2}$)$^{2}$ + 3($\frac{1}{2}$) + 1

                  = $\frac{1}{8}$ + $\frac{3}{4}$ + $\frac{3}{2}$ + 1

                  = $\frac{1 + 6 + 12 + 8}{8}$

                  = $\frac{27}{8}$

(iii) Let f(x) = x$^{3}$ + 3x$^{2}$ + 3x +1, divisor is x i.e., x - 0

Then by the Remainder Theorem we get,

Remainder = f(0)

                  = 0$^{3}$ + 3 ∙ 0$^{2}$ + 3 ∙  0 + 1

                  = 1

(iv) Let f(x) = x$^{3}$ + 3x$^{2}$ + 3x +1, divisor is x + γ

Then by the Remainder Theorem we get,

Remainder = f(-γ)

                  = (-γ)$^{3}$ + 3(-γ)$^{2}$ + 3(-γ) +1

                  = -γ$^{3}$ + 3γ$^{2}$ - 3γ +1

(v) Let f(x) = x$^{3}$ + 3x$^{2}$ + 3x +1, divisor is 5 + 2x

Then by the Remainder Theorem we get,

Remainder = f(-$\frac{5}{2}$)

                   = (-$\frac{5}{2}$)$^{3}$ + 3(-$\frac{5}{2}$)$^{2}$ + 3(-$\frac{5}{2}$) + 1

                   = $\frac{-125}{8}$ + $\frac{75}{4}$ - $\frac{15}{2}$ + 1

                   = $\frac{-125 + 150 -60 + 8}{8}$

                   = -$\frac{27}{8}$

2. If 3x$^{2}$ - 7x + 11 is divided by x - 2 then find the remainder.

Solution:

Here p(x) = 3x$^{2}$ - 7x + 11, divisor is x - 2

Therefore, remainder = p(2)                    [Taking x = 2 from x - 2 = 0]

                                   = 3(2)$^{2}$ - 7(2) + 11

                                   = 12 - 14 + 11

                                   = 9

● Factorization

• Polynomial
• Polynomial Equation and its Roots
  
• Division Algorithm
  
• Remainder Theorem
  
• Problems on Remainder Theorem
  
• Factors of a Polynomial
  
• Worksheet on Remainder Theorem
  
• Factor Theorem
  
• Application of Factor Theorem

10th Grade Math

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