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How to find the roots of a quartic polynomial?

To determine the roots of a quartic polynomial, we have two primary methods: using the quartic formula or factorization.

The quartic formula is a comprehensive and intricate expression that can be applied to find the roots of any quartic polynomial. It is expressed as:

x=b±b24ac2ad22aorx=b±i4ad2b2+2ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac - 2ad^2}}{2a} \quad \text{or} \quad x = \frac{-b \pm i\sqrt{4ad^2 - b^2 + 2ac}}{2a}

In this equation, aa, bb, cc, and dd represent the coefficients of the quartic polynomial in the standard form ax4+bx3+cx2+dx+eax^4 + bx^3 + cx^2 + dx + e. While this formula can yield the desired roots, it can be cumbersome, particularly when dealing with large or complex coefficients. A deeper understanding of this formula may provide valuable insights into managing such intricate calculations.

Alternatively, we can simplify the process by factorizing the quartic polynomial into two quadratic factors, which can then be solved using the quadratic formula. This approach is generally more straightforward and quicker than applying the quartic formula. Various techniques, such as grouping, substitution, or trial and error, can be utilized for factorization. Gaining familiarity with these methods can enhance your understanding of factorization in higher-dimensional equations.

For instance, let’s consider the quartic polynomial x45x2+4x^4 - 5x^2 + 4. We can factor it as follows:

(x24)(x21)=0(x^2 - 4)(x^2 - 1) = 0

Next, we apply the quadratic formula to find the roots of each quadratic factor:

  1. For x24=0x^2 - 4 = 0, we get:

    x=±2x = \pm 2
  2. For x21=0x^2 - 1 = 0, we find:

    x=±1x = \pm 1

Consequently, the roots of the quartic polynomial are x=±2x = \pm 2 and x=±1x = \pm 1. For those interested in the calculus and underlying principles involved in solving such equations, exploring related mathematical concepts could be highly beneficial.

In summary, to find the roots of a quartic polynomial, you can either utilize the complex quartic formula or factor it into simpler quadratic equations. The quartic formula entails a meticulous calculation involving the coefficients aa, bb, cc, and dd. On the other hand, factorization allows us to break the polynomial down into more manageable components, ultimately leading to simpler solutions. For example, the polynomial x45x2+4x^4 - 5x^2 + 4 can be factored to reveal the roots x=±2x = \pm 2 and x=±1x = \pm 1.

Answered by: Prof. Isabella Taylor
A-Level Maths Tutor
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