Chapter 1: Problem 9
Find the polynomial with the smallest degree that goes through the given points. $$(-4,-3),(0,1) \text { and }(1,4.5)$$
Short Answer
Expert verified
The polynomial is \( P(x) = 0.5x^2 + 3x + 1 \).
Step by step solution
01
Determine Polynomial Form
To find a polynomial that passes through given points, assume the smallest-degree polynomial. For three points, start with a quadratic polynomial of the form \[ P(x) = ax^2 + bx + c. \]
02
Set Up the Equation System
Use the given points to create a system of equations. Substitute each point into the polynomial equation:\[ P(-4) = a(-4)^2 + b(-4) + c = -3 \P(0) = a(0)^2 + b(0) + c = 1 \P(1) = a(1)^2 + b(1) + c = 4.5.\] This simplifies to:\[ 16a - 4b + c = -3 \c = 1 \a + b + c = 4.5.\]
03
Solve the Equation System
Substitute \( c = 1 \) into the other equations:\[16a - 4b + 1 = -3 \a + b + 1 = 4.5.\]Rearrange these to:\[16a - 4b = -4 \a + b = 3.5.\]Solve these equations using substitution or elimination. Here, we notice:\[b = 3.5 - a.\]Substitute in the first:\[16a - 4(3.5 - a) = -4 \16a - 14 + 4a = -4 \20a = 10 \a = 0.5.\]
04
Find Remaining Coefficients
Substitute \( a = 0.5 \) back to find \( b \):\[b = 3.5 - 0.5 = 3.\]
05
Write the Polynomial
Substitute the values of \( a \), \( b \), and \( c \) back into the polynomial form:\[ P(x) = 0.5x^2 + 3x + 1. \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quadratic Polynomial
A quadratic polynomial is a polynomial of degree two, which means that its highest power of the variable is squared. The general form of a quadratic polynomial is given by: \[ P(x) = ax^2 + bx + c \] where:
- a, b, and c are constants with a not equal to zero.
- x is the variable.
System of Equations
A system of equations refers to a set of multiple equations that are solved together since they share common variables. In solving for the coefficients of a quadratic polynomial passing through given points, you create a system of linear equations by plugging the points into the polynomial expression. For example:
- Using point \((-4, -3)\), we have: \(16a - 4b + c = -3\).
- Using point \((0, 1)\), we simplify to \(c = 1\).
- Using point \((1, 4.5)\), the equation is \(a + b + c = 4.5\).
Substitution Method
The substitution method is a technique used for solving systems of equations where one equation is solved for one variable, and then this expression is substituted into other equations. Here's how it generally works:
- First, isolate one variable in one of the simpler equations. For instance, in the equation \(c = 1\), \(c\) is already isolated.
- Substitute \(c = 1\) into the other equations: \(16a - 4b + 1 = -3\) and \(a + b + 1 = 4.5\).
- This substitution simplifies the system, leaving you with a reduced number of equations with fewer variables. Solve these step by step.
Elimination Method
The elimination method involves manipulating equations in a system to eliminate one of the variables, making it easier to solve the remaining equations. Here's a step-by-step idea of how it is applied:
- First, ensure the equations are lined up with variables and constants matched in order.
- Choose a variable to eliminate and manipulate the equations to make the coefficients of this variable equal in magnitude but opposite in sign across two equations.
- For example, from \(16a - 4b = -4\) and using \(b = 3.5 - a\) obtained from another equation, there's a simplified way of seeing \(20a = 10\).
- This leads to finding \(a = 0.5\) and allowing substitution into a simplified remaining equation to find the other variables.