Chapter 6: Problem 6
Test the sets of polynomials for linear independence. For those that are linearly dependent, express one of the polynomials as a linear combination of the others. $$\left\\{1+x, 1+x^{2}, 1-x+x^{2}\right\\} \text { in } \mathscr{P}_{2}$$
Short Answer
Expert verified
The set of polynomials is linearly independent.
Step by step solution
01
Understand the Problem
We need to determine if the given set of polynomials \( \{1+x, 1+x^{2}, 1-x+x^{2}\} \) in \( \mathscr{P}_{2} \) are linearly independent. If they are dependent, we must express one polynomial as a linear combination of the others.
02
Set Up the Linear Combination
Assume that a linear combination of these polynomials equals zero: \( a(1+x) + b(1+x^2) + c(1-x+x^2) = 0 \) for some scalars \( a, b, c \).
03
Expand and Combine Like Terms
Expand and combine like terms to get: \( (a+b+c) + ax - cx + (b+c)x^2 = 0 \). This must hold for all values of \( x \), so each coefficient must equal zero.
04
Set Up Equations for Coefficients
From the linear combination, we have the system of equations: \[ a + b + c = 0 \] \[ a - c = 0 \] \[ b + c = 0 \].
05
Solve the System of Equations
Using the equation \( a - c = 0 \), we have \( a = c \). Substitute this into \( b + c = 0 \) to get \( b = -c \). Substitute into \( a + b + c = 0 \) to find \( c = 0 \), and thus \( a = 0 \), \( b = 0 \).
06
Interpret the Results
Since the only solution is the trivial solution \( a = 0 \), \( b = 0 \), \( c = 0 \), the polynomials are linearly independent. Therefore, no polynomial can be expressed as a linear combination of the others.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Linear Combination
A linear combination is a mathematical concept where we express a function or vector as a sum of multiples of other functions or vectors. In our exercise, we examine if a polynomial can be written as a linear combination of other polynomials. Specifically, we check if coefficients exist such that:
This makes a linear combination an essential tool for determining the linear independence of a set of functions or vectors.
Key steps in understanding linear combinations:
- \( a(1+x) + b(1+x^2) + c(1-x+x^2) = 0 \)
This makes a linear combination an essential tool for determining the linear independence of a set of functions or vectors.
Key steps in understanding linear combinations:
- Express the set functions as a weighted sum.
- Solve for the coefficients (scalars) that make this sum equal zero.
- Identify if only a trivial solution (all scalars equal zero) exists.
Polynomials
Polynomials are expressions made up of variables and coefficients, where the variables are raised to whole-number exponents. In our exercise, we deal with polynomials like \( 1+x \), \( 1+x^2 \), and \( 1-x+x^2 \) within the polynomial space \( \mathscr{P}_{2} \).
Understanding polynomials involves knowing:
Given polynomials help us explore wider mathematical concepts like independence and dependence in a polynomial context.
Understanding polynomials involves knowing:
- Terms: Individual parts of polynomials, such as \( x^2 \).
- Coefficients: Numbers multiplying the variables, in expressions like \( 1 \) in \( 1+x \).
- Degree: The highest exponent of the variable, indicating the polynomial's order.
Given polynomials help us explore wider mathematical concepts like independence and dependence in a polynomial context.
System of Equations
A system of equations consists of multiple equations that are solved together, which means finding values for variables that satisfy all the equations simultaneously. During the exercise, we arrange a system from the coefficients of the polynomials to explore their independence:
To solve a system of equations, follow these steps:
- \( a + b + c = 0 \)
- \( a - c = 0 \)
- \( b + c = 0 \)
To solve a system of equations, follow these steps:
- Isolate variables using substitution or elimination methods.
- Simplify until you deduce the values of variables that meet all equations.
- Identify the solution types — notably, the trivial solution suggests independence.