Solving Higher-Degree Polynomials by Synthetic Division and the Rational Roots Test

Professor Dave Explains
28 Sept 201709:22
EducationalLearning
32 Likes 10 Comments

TLDRThe video explains techniques to solve complex polynomial equations, like synthetic division to test if a number is a solution and can factor the polynomial. It first establishes prime polynomials and need for factorization. Synthetic division is then illustrated, showing how remainder indicates if a number is a solution. An example quartic equation is solved using possible rational roots. More examples demonstrate synthetic division, factoring polynomials when solutions are found. Finally, the rational roots test is explained to generate possible solutions to try when solving higher degree polynomials with synthetic division.

Takeaways
  • πŸ˜€ Synthetic division is a technique to test if a polynomial is divisible by a linear factor
  • πŸ˜‡ It works similarly to long division, but with algebraic expressions instead of numbers
  • 🧐 Prime polynomials can't be factored further, others can be split into factors
  • 😏 The rational roots test generates possible solutions to test with synthetic division
  • πŸ€“ Remainder of 0 after synthetic division means the number tested is a solution
  • 😎 Solutions found allow splitting the polynomial into linear factors
  • πŸ₯Έ Quartic/quintic equations can be solved by testing factors from the rational roots test
  • πŸ€” No remainder means a factor was found; remainder means to try another factor
  • πŸ’‘ Can continue factoring completely with synthetic division until only binomials left
  • πŸ₯³ So synthetic division determines if polynomials have certain linear factors
Q & A
  • What are prime polynomials and how are they similar to prime numbers?

    -Prime polynomials are polynomials that cannot be factored into other polynomials, just as prime numbers cannot be factored into other whole numbers except 1 and themselves. So prime polynomials are the building blocks of other polynomial expressions.

  • What is synthetic division and how does it allow us to test if a polynomial is divisible by a particular expression?

    -Synthetic division is an algebraic technique similar to long division that allows us to test if a polynomial is divisible by a linear factor. We set up the coefficients in a particular way and go through a process of multiplying and adding to see if we get a remainder of 0, which would indicate the polynomial is divisible by the linear factor being tested.

  • How can we generate a list of possible rational roots to test when using synthetic division?

    -We can use the rational roots test to generate a list of possible rational roots. This involves making fractions with the factors of the constant term in the numerator and factors of the leading coefficient in the denominator. We test these rational numbers as possible roots using synthetic division.

  • What happens if we get a non-zero remainder when performing synthetic division on a polynomial?

    -If we get a non-zero remainder, that indicates that the linear factor we are testing is not actually a factor of the polynomial. In other words, the number we tried does not generate a root for the polynomial.

  • How does synthetic division allow us to simplify a polynomial expression?

    -When a linear factor tests successfully as a root, we can split the original polynomial into that linear factor and a lower degree polynomial found from the coefficients generated during synthetic division. This lets us break down complex polynomials into simpler factorized forms.

  • What types of polynomials can synthetic division help solve that other algebraic techniques cannot?

    -Synthetic division is particularly helpful for solving for the roots of high degree polynomials such as cubics, quartics, and quintics. Factoring techniques tend to fail for polynomials higher than quadratics, so synthetic division gives us a way to find roots of very complex polynomials.

  • If none of the possibilities from the rational roots test end up being actual roots, what does that tell us?

    -If none of the rational root possibilities generate a root, that tells us the polynomial likely does not have any rational roots. So we would have to explore other techniques like graphing or approximations to find any irrational or complex roots.

  • What is the benefit of fully factorizing a polynomial using synthetic division?

    -Fully factorizing gives us all the linear factors that represent the roots of the polynomial. Having the expression written in completely factored form allows us to clearly identify all the zeroes, make connections to any graphs, and know we have found all solutions.

  • How does the process help us solve quartic and quintic equations that we otherwise could not solve algebraically?

    -Quartic and quintic equations generally cannot be solved fully algebraically except in some special cases. But synthetic division gives us a methodical way to test possible roots through an algebraic, computational process until we have found all the linear factors that make up the polynomial.

  • What math concepts from earlier in algebra does synthetic division build upon?

    -Synthetic division relies heavily on concepts like long division, factoring, polynomial arithmetic, and the remainder theorem. So it assumes knowledge of working with polynomials, but takes those skills to address more complex polynomial equations.

Outlines
00:00
πŸ˜€ Introducing Synthetic Division for Polynomials

Paragraph 1 introduces the concept of synthetic division, explaining how it is used to determine if a polynomial is divisible by a particular expression. It draws parallels to prime factorization of numbers and finding factors of polynomials. Synthetic division works similarly to long division, but uses algebraic expressions instead of numbers. An example quartic polynomial is used to demonstrate the technique and show how it allows solving for all possible solutions.

05:04
πŸ˜ƒ Using Rational Roots Test to Find Possible Solutions

Paragraph 2 explains the rational roots test, which generates a list of possible solutions to try when using synthetic division. It provides the process for constructing the list of options by looking at factors of the leading and constant terms. An example cubic polynomial is then used to demonstrate trying values from the list to see if they are solutions via synthetic division. Ultimately three solutions are found.

Mindmap
Keywords
πŸ’‘polynomial
A polynomial is an algebraic expression made up of terms that each have variables raised to positive integer exponents. Polynomials are a key concept in the video, as Professor Dave is teaching methods to solve and factor different types of polynomials. He starts by relating polynomial factorization to prime factorization of numbers.
πŸ’‘factor
To factor means to express a quantity as a product of other quantities. The video focuses on factoring polynomials to find the solutions, using things like synthetic division. Factoring allows polynomials to be broken down into simpler binomial factors.
πŸ’‘synthetic division
Synthetic division is a technique used to efficiently divide polynomials, similar to long division for numbers. It tests whether a polynomial is divisible by a linear factor. The method involves arranging coefficients in rows, multiplying, and adding to check for a remainder of 0.
πŸ’‘zero
A zero of a polynomial is a solution - a value that makes the polynomial equal 0 when substituted. Synthetic division tests potential linear factors to see if they yield a 0 remainder, indicating a zero has been found.
πŸ’‘quadratic
A quadratic polynomial has the highest exponent of 2. The video shows how synthetic division can simplify a higher order (cubic, quartic) polynomial down to a quadratic or lower for easier solving.
πŸ’‘cubic
A cubic polynomial has the highest exponent of 3. Synthetic division is very useful for solving cubics when you already know one zero.
πŸ’‘quartic
A quartic polynomial has the highest exponent of 4. The technique is illustrated on a quartic in the video. Synthetic division can reduce it to a cubic.
πŸ’‘rational roots
The rational roots test gives possible rational solutions to try to make the synthetic division process more efficient. You take factors of coefficients to get numerator and denominator.
πŸ’‘remainder
The remainder in synthetic division indicates whether division was successful. A remainder of 0 means the linear factor evenly divided the polynomial, so that value is a zero.
πŸ’‘binomial
A binomial is a two-term polynomial. Factoring using synthetic division splits higher order polynomials into binomial factors.
Highlights

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