Chapter 3: Problem 29
The polynomial \(p(x)=(a x+b)^{3}\) leaves a remainder of -1 when divided by \(x+1,\) and a remainder of 27 when divided by \(x-2 .\) Find the values of the real numbers \(a\) and \(b\)
Short Answer
Expert verified
The values are \( a = \frac{4}{3} \) and \( b = \frac{1}{3} \).
Step by step solution
01
Understand the Remainder Theorem
According to the Remainder Theorem, if a polynomial \( p(x) \) is divided by \( x-c \), the remainder is \( p(c) \). Therefore, for \( (a x + b)^3 \) divided by \( x+1 \), the remainder is \( p(-1) = -1 \). Similarly, for division by \( x-2 \), the remainder is \( p(2) = 27 \).
02
Set Up Equations Using the Remainder Theorem
Substitute \( x = -1 \) into \( p(x) = (a x + b)^3 \). This results in \( (a(-1) + b)^3 = -1 \) or \( (-a + b)^3 = -1 \). Similarly, substitute \( x = 2 \) to get \( (a(2) + b)^3 = 27 \) or \( (2a + b)^3 = 27 \).
03
Solve the System of Equations
Solve the first equation \((-a + b)^3 = -1\). Taking the cube root of both sides gives \(-a + b = -1\). Solve the second equation \((2a + b)^3 = 27\). Taking the cube root of both sides gives \(2a + b = 3\). Now you have a system of linear equations: \(-a + b = -1\) and \(2a + b = 3\).
04
Combine and Solve for b
From \(-a + b = -1\), solve for \(b\): \(b = a - 1\). Substitute \(b = a - 1\) into the second equation: \(2a + (a - 1) = 3\). Solve for \(a\) by simplifying the equation: \(3a - 1 = 3\).
05
Find the Value of a
Solve the equation \(3a - 1 = 3\) to find \(a\). Adding 1 to both sides gives \(3a = 4\). Divide by 3 to get \(a = \frac{4}{3}\).
06
Substitute to Find b
Substitute \(a = \frac{4}{3}\) into the equation \(b = a - 1\). This results in \(b = \frac{4}{3} - 1 = \frac{4}{3} - \frac{3}{3} = \frac{1}{3}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Division
Polynomial division is an essential concept in algebra that involves dividing a polynomial by another polynomial. When we divide a polynomial by a linear divisor of the form \(x - c\), the Remainder Theorem becomes particularly useful. It's a theorem that helps simplify the division by directly providing the remainder.In the example exercise, we are using the polynomial \(p(x) = (ax + b)^3\). It's divided by two different linear divisors, \(x+1\) and \(x-2\). The Remainder Theorem tells us that the remainder of the division of \(p(x)\) by \(x-c\) is \(p(c)\). Thus:
- When divided by \(x+1\), we find the remainder by calculating \(p(-1)\).
- When divided by \(x-2\), we calculate \(p(2)\) to find the remainder.
System of Equations
A system of equations is a set of multiple equations that are all solved together. In this exercise, we deal with a system of two equations derived from the Remainder Theorem results.To solve the problem, we obtain the following two equations:
- \((-a + b)^3 = -1\), simplifying to \(-a + b = -1\).
- \((2a + b)^3 = 27\), simplifying to \(2a + b = 3\).
Linear Equations
Linear equations are equations of the first degree, meaning each term is either a constant or the product of a constant and a single variable. In the context of our exercise, both \(-a + b = -1\) and \(2a + b = 3\) are linear equations.Solving these involves standard techniques:
- First, solve one equation for one variable, such as solving \(-a + b = -1\) for \(b\), leading to \(b = a - 1\).
- Substituting this expression into the second equation \(2a + b = 3\) helps eliminate \(b\).