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What is the remainder theorem?
alphonsio

ThePolynomial Remainder Theorem states that if a polynomial f(x)f(x) is divided by a linear divisor of the form x−cx - c, then the remainder of this division is simply f(c)f(c).

f(x)=(x−c)⋅Q(x)+Rf(x) = (x - c) \cdot Q(x) + R

where Q(x)Q(x) is the quotient polynomial and RR is the remainder, the theorem tells us that:

R=f(c)R = f(c)


The Polynomial Remainder Theorem states that if a polynomial f(x)f(x) is divided by a linear divisor (x−c)(x - c), then the remainder of this division is simply f(c)f(c). In other words:

f(x)=(x−c)Q(x)+Rf(x) = (x - c) Q(x) + R

where:

  • Q(x)Q(x) is the quotient,
  • RR is the remainder.

Since the divisor (x−c)(x - c) is a linear polynomial, the remainder must be a constant. The theorem asserts that this constant remainder is just f(c)f(c).

Additionally, if the remainder RR is zero, then x−cx - c is a factor of the polynomial f(x)f(x), which is related to the Factor Theorem.

Example:

Let’s say we have the polynomial:

f(x)=x3−4x+6f(x) = x^3 - 4x + 6

If we divide f(x)f(x) by (x−2)(x - 2), then the remainder is found by evaluating f(2)f(2):

f(2)=(2)3−4(2)+6=8−8+6=6f(2) = (2)^3 - 4(2) + 6 = 8 - 8 + 6 = 6

So, the remainder when dividing f(x)f(x) by (x−2)(x - 2) is 6.

In this example, Q=x2+2xQ=x^2+2x. Thus, we can express the division as:

f(x)=(x−2)(x2+2x)+6f(x) = (x - 2)(x^2 + 2x) + 6

This theorem is particularly useful in polynomial division and checking factors using the Factor Theorem, which is a direct consequence of the Remainder Theorem.