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When \(f(x)\) is divided by \((x-a)(x-b),\) the remainder is \(A x+B .\) Apply the division algorithm to show that $$A=\frac{f(a)-f(b)}{a-b} \quad \text { and } \quad B=\frac{b f(a)-a f(b)}{b-a}$$

Short Answer

Expert verified
\( A = \frac{f(a) - f(b)}{a-b} \) and \( B = \frac{b f(a) - a f(b)}{b-a} \).

Step by step solution

01

Understand the Problem

When a function \( f(x) \) is divided by a quadratic polynomial \( (x-a)(x-b) \), we can express this using the polynomial division algorithm. According to the algorithm, \( f(x) = (x-a)(x-b)Q(x) + Ax + B \), where \( Q(x) \) is the quotient and \( Ax+B \) is the remainder.
02

Evaluate the Function at Roots

To find \( A \) and \( B \), evaluate \( f(x) \) at \( x = a \) and \( x = b \). This will give us two equations because the remainder must be the same when substituting roots of the divisor.\( f(a) = A(a) + B \) and \( f(b) = A(b) + B \).
03

Set Up a System of Equations

From step 2, you get two equations: \( f(a) = Aa + B \) and \( f(b) = Ab + B \). These linear equations can be used to solve for \( A \) and \( B \).
04

Solve for A

From equations \( f(a) = Aa + B \) and \( f(b) = Ab + B \), subtract the latter from the former: \( f(a) - f(b) = Aa + B - (Ab + B) \), simplifying to \( f(a) - f(b) = A(a-b) \). So, \( A = \frac{f(a) - f(b)}{a-b} \).
05

Solve for B

Use any of the two equations from step 3 to solve for \( B \). Let's use \( f(a) = Aa + B \). Substitute \( A \) from the previous step: \( f(a) = \frac{f(a) - f(b)}{a-b}a + B \). Rearrange to find \( B \): \( B = f(a) - \frac{f(a) - f(b)}{a-b}a \). Simplify using common denominators to find \( B = \frac{bf(a) - af(b)}{b-a} \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Division Algorithm
Let's delve into the concept of the Division Algorithm, particularly as it applies to polynomials. In essence, the division algorithm for polynomials states that when a polynomial \( f(x) \) is divided by a divisor \( (x-a)(x-b) \), it can be expressed in the general form:
  • \( f(x) = (x-a)(x-b)Q(x) + R(x) \)
Here, \( Q(x) \) is the quotient, which is a polynomial, and \( R(x) \) is the remainder. The degree of the remainder \( R(x) \) must be less than the degree of the divisor. Since \( (x-a)(x-b) \) is a quadratic polynomial, \( R(x) \) is at most linear, hence it takes the form \( Ax + B \).
By using this structure, we can then solve for unknown coefficients such as \( A \) and \( B \) if certain conditions are met. It simplifies complex polynomial problems by allowing them to be broken down into parts via division.
Understanding this is crucial as it sets the stage for calculating remainders and solving polynomials effectively.
Remainder Theorem
The Remainder Theorem is a fundamental principle when dealing with polynomial division. It simplifies the process of finding the remainder of a polynomial when divided by a linear divisor. According to the theorem:
  • When a polynomial \( f(x) \) is divided by a linear divisor \( x-a \), the remainder of this division is \( f(a) \).
This theorem means that instead of performing full polynomial division, you can quickly find the remainder just by substituting the value of \( a \) into the polynomial.
Applying this theorem to our exercise, you see that when \( f(x) \) is divided by \((x-a)(x-b)\) and gives a remainder of \( Ax + B \), we utilize the criteria that \( f(x) \) evaluated at \( x=a \) and \( x=b \) helps set up useful equations.\[ f(a) = Aa + B \]
\[ f(b) = Ab + B \]
These equations are crucial for solving \( A \) and \( B \) and illustrate the intersection of polynomial division and remainder calculations.
System of Equations
A system of equations arises when you have multiple equations that are interrelated and share common variables. In the context of our polynomial division exercise, we are presented with:
  • \( f(a) = Aa + B \)
  • \( f(b) = Ab + B \)
These equations form a system because they both need to satisfy the values of the polynomial flanked by the points \( a \) and \( b \). Solving such a system involves finding values of \( A \) and \( B \) that satisfy both equations simultaneously.
To do this, we can subtract one equation from another, eliminating one of the variables in order to solve for the other one. Once you have one variable, substitute back into one equation to solve for the other.
This method demonstrates how systems of equations can be utilized to simplify and resolve polynomial problems by isolating and deducing unknown variables.
Polynomial Functions
Polynomial functions are expressions consisting of variables and coefficients, structured in terms of powers.
  • They can take various forms such as linear \((Ax + B)\), quadratic \((ax^2 + bx + c)\), and higher degrees.
These functions are central in the study of algebra and calculus due to their diverse applications. In this exercise, \(f(x)\) represents a polynomial function that is divided to demonstrate key fundamentals.
Such functions present interesting characteristics like roots, which are values of \(x\) that make \(f(x) = 0\). These roots are leveraged when dividing polynomials to simplify expressions and understand behaviors of graphs.
Additionally, understanding polynomial functions' end behaviors, zeros, and transformations are essential in predicting how they are graphically represented and how they interact during operations like division. This provides a holistic view of polynomial operations within mathematical progressions.

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Most popular questions from this chapter

Consider the equation \(x^{3}+p x-q=0,\) where \(p\) and \(q\) are prime numbers. Observe that there are only four possible rational roots here: \(1,-1, q,\) and \(-q\) (a) Show that if \(x=1\) is a root, then we must have \(q=3\) and \(p=2 .\) What are the remaining roots in this case? (b) Show that none of the numbers \(-1, q,\) and \(-q\) can be a root of the equation. Hint: For each case, assume the contrary, and deduce a contradiction.

Determine the partial fraction decomposition for each of the given expressions. $$\frac{1}{(x-a)(x+a)} \quad(a \neq 0)$$

(a) Use a calculator to verify that the number \(\tan 9^{\circ}\) appears to be a root of the following equation: $$ x^{4}-4 x^{3}-14 x^{2}-4 x+1=0 $$ In parts (b) through (d) of this exercise, you will prove that \(\tan 9^{\circ}\) is indeed a root and that \(\tan 9^{\circ}\) is irrational. (b) Use the trigonometric identity $$ \tan 5 \theta=\frac{\tan ^{5} \theta-10 \tan ^{3} \theta+5 \tan \theta}{5 \tan ^{4} \theta-10 \tan ^{2} \theta+1} $$ to show that the number \(x=\tan 9^{\circ}\) is a root of the fifth-degree equation $$ x^{5}-5 x^{4}-10 x^{3}+10 x^{2}+5 x-1=0 $$Hint: In the given trigonometric identity, substitute \(\theta=9^{\circ}\) (c) List the possibilities for the rational roots of equation (2). Then use synthetic division and the remainder theorem to show that there is only one rational root. What is the reduced equation in this case? (d) Use your work in parts (b) and (c) to explain (in complete sentences) why the number \(\tan 9^{\circ}\) is an irrational root of equation (1).

This exercise completes the discussion of improper rational expressions in this section. (a) Use long division to obtain the following result: \(\frac{2 x^{3}+4 x^{2}-15 x-36}{x^{2}-9}=(2 x+4)+\frac{3 x}{x^{2}-9}\) (b) Find constants \(A\) and \(B\) such that \(3 x /\left(x^{2}-9\right)=A /(x-3)+B /(x+3) .\) (According to the text, you should obtain \(A=B=3 / 2 .\) )

Find all roots of each equation. Hints: First, factor by grouping. In Exercises 71 and 72 each equation has three roots; in Exercise 73 the equation has six roots; in Exercise 74 there are five roots. $$x^{5}+4 x^{3}+8 x^{2}+32=0$$

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