Chapter 15: Problem 11
Let \(f=x^{3}-292 x^{2}-2170221 x+6656000 \in \mathbb{Z}[x]\). Find 13 -adic linear factors \(x-a_{i}\) with \(f\) rem \(x-a_{i} \equiv 0 \bmod 13^{2}\) for \(i=0,1,2\), starting with \(a_{0}=0\).
Short Answer
Expert verified
Factors are \(x, x-1, x-2\) modulo 13.
Step by step solution
01
Begin with Initial Remainder Modulo 13
Since we start with \(a_0 = 0\), find the remainder when \(f(x)\) is divided by \(13\).Substitute \(x = 0\) into the polynomial:\[f(0) = 0^3 - 292 \times 0^2 - 2170221 \times 0 + 6656000 = 6656000.\]Now find the remainder of 6656000 modulo 13 to start the analysis:\[ 6656000 \mod 13 = 0.\]This confirms that \(x - 0\) is a factor modulo 13.
02
Find First Linear Factor for \(a_1\) Modulo 13
To find \(a_1\), substitute different values into \(f(x)\) to find another factor. Suppose \(x = 1\) and calculate:\[f(1) = 1^3 - 292 \times 1^2 - 2170221 \times 1 + 6656000.\]Calculate this result modulo 13:\[f(1) = 1 - 292 - 2170221 + 6656000.\]We simplify: 6656000 - 292 - 2170221 + 1 = 4484488.Now, calculate \(4484488 \equiv 0 \mod 13\).Since this is congruent, \(x - 1\) is another linear factor modulo 13.
03
Confirm Factors Modulo 13
Having found \(x - 0\) and \(x - 1\) as factors for modulo 13, verify these results. Since both give results \(f(0) \equiv 0 \mod 13\) and \(f(1) \equiv 0 \mod 13\), check for another possible \(a_2\). Try \(x = 2\):\[f(2) = (2)^3 - 292 \times (2)^2 - 2170221 \times 2 + 6656000.\]Calculate modulo 13:4484424 \(\equiv 0 \mod 13\).Therefore, \(x - 2\) is another factor.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
13-adic numbers
When delving into polynomial equations, you might encounter the concept of *'adic' numbers*, such as the 13-adic numbers. These are a fascinating way to look at numbers through the lens of modular arithmetic. Instead of our usual decimal system, we base our views on a particular modulus, in this case, 13. Here's how it works:
- The 13-adic numbers focus on congruence and continuity, similar to how real numbers consider infinite precision in decimals.
- They express numbers as an infinite series, where each coefficient is determined by the modulus, here 13.
- Imagine stacking infinitesimal layers onto integers, providing a unique perspective on calculations.
Linear factors
Linear factors are the building blocks of polynomial factorization. They are expressions of the form \(x - a\), representing a root of a polynomial. Let's break this down:
- For a polynomial \(f(x)\), if \((x - a)\) is a factor, \(f(a) = 0\), meaning \(a\) is a root.
- Finding linear factors involves expressing the polynomial as a product of these factors, revealing its roots.
- In the context of 13-adic factorization, each linear factor fits within the conditions of congruence, often calculated modulo different powers of 13.
Modulo arithmetic
In mathematics, *modulo arithmetic* is essential for understanding situations where only remainders matter. It's particularly handy in number theory and cryptography. Here's a simple breakdown:
- Modulo arithmetic focuses on the remainder after division by a specified number, called the modulus. For instance, \(17 \mod 5 = 2\) because dividing 17 by 5 leaves a remainder of 2.
- This becomes a tool to simplify numerical expressions by focusing on equivalence rather than exact equality.
- In our exercise, we use modulo 13 to assess the factors of the polynomial by determining which values make the polynomial function equal to zero.*
Factor theorem
The Factor Theorem is a cornerstone in polynomial algebra. It establishes a relationship between the roots of polynomials and their factors. Here's a concise look:
- According to the theorem, if \(f(a) = 0\), then \(x-a\) is a factor of the polynomial \(f(x)\).
- This provides a systematic way to identify and confirm roots.
- It's especially powerful in coordinate with the Remainder Theorem, which says the remainder of \(f(x)\) divided by \((x-a)\) is \(f(a)\).