45. Polynomials - JulTob/Mathematics GitHub Wiki

Polynomials

A polynomial function is defined as a linear combination of the powers of the variable (usually $x$)

$$P(x) = a_0 + a_1x + a_2x^2 ⠀.+.⠀ a_nx^n$$ $$P(x) = ∑_0^n a_ix^i$$
  • $a_i$ are the coefficients
  • Each $a_ix^i$ are the terms

Quadratic Functions

A quadratic function is a polynomial function of 2nd degree.

$$f(x) = c + b·x + a· x^2$$

Normal Form

The normal form of a quadratic function is of the form

$$f(x) = a(x-h)^2 + k$$ Screenshot 2023-03-30 at 12 38 44

We see there's a maximum/minimum point at $x=h$

  • If $a>0$, then the minimum of $f$ is $f(h)=k$
  • If $a<0$, then the maximum of $f$ is $f(h)=k$

Maximum or minimum

The apex point (maximum or minimum of a parabola) can be calculated from the standard form $ax^2+bx+c$, and is located at

$$x = - \frac{b}{2a}$$
  • If $a>0$, then it is a minimum of $f$.
  • If $a<0$, then it is a maximum of $f$.

Polynomical zeros

A zero $c_i$ is each point of a polynomial that satisfies $f(c_i) = 0$

  • They are solutions to $𝐏[x]=0$

Polynomial Plots

  1. Ceros. Factorizar la polinomial para hallar todos sus ceros reales; éstos son los puntos de intersección x de la gráfica.
  2. Puntos de prueba. Hacer una tabla de valores para la polinomial. Incluir puntos de prueba para determinar si la gráfica de la polinomial se encuentra arriba o abajo del eje x sobre los intervalos determinados por los ceros. Incluir el punto de intersección y en la tabla.
  3. Comportamiento final. Determinar el comportamiento final de la polinomial.
  4. Graficar. Localizar los puntos de intersección y otros puntos que se encuen- tren en la tabla. Trazar una curva sin irregularidades que pase por estos puntos y exhibir el comportamiento final requerido

Maths

xychart-beta
    title "x to the power of 3"
    x-axis "x" -10 --> 10
    x-axis [-10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    y-axis "y" -1000 --> 1000
    line [-1000, -729, -512, -343, -216, -125, -64, -27, -8, -1, 0, 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]

Loading
🐍 Python Code:
  def generate_xychart(start, end, power):
    """
    Generates a custom XY chart format for x raised to a specified power.

    Args:
        start (int): Start of the range (inclusive).
        end (int): End of the range (inclusive).
        power (int): The power to which x is raised.

    Returns:
        str: The XY chart representation as a string.
    """
    # Generate x values
    x_values = list(range(start, end + 1))
    # Generate corresponding y values
    y_values = [x ** power for x in x_values]

    # Format the chart output
    chart_output = (
        f"xychart-beta\n"
        f"    title \"x to the power of {power}\"\n"
        f"    x-axis \"x\" {min(x_values)} --> {max(x_values)}\n"
        f"    x-axis {x_values}\n"
        f"    y-axis \"y\" {min(y_values)} --> {max(y_values)}\n"
        f"    line {y_values}"
    )

    return chart_output

  # Example usage
  start_range = -10
  end_range = 10
  power_value = 3
  chart = generate_xychart(start_range, end_range, power_value)
  print(chart)

Binomial Theorem

$$(𝑥+𝑦)² = 𝑥² + 2𝑥𝑦 + 𝑦²$$ $$(𝑥+𝑦)³ = 𝑥³ + 3𝑥²𝑦 + 3𝑥𝑦² + 𝑦³$$ $$(𝑥+𝑦)ⁿ = 𝑥³ + 3𝑥²𝑦 + 3𝑥𝑦² + 𝑦³$$ $$\sum_{i=1..n,k=1+n -i}\begin{pmatrix} n \\\ k \end{pmatrix} x^{n-i}y^i$$ $$\begin{pmatrix} n \\\ k \end{pmatrix} = ∏_1^k (n-k+1) / ∏_1^k i$$ $$(𝑥-𝑦)² = 𝑥² - 2𝑥𝑦 + 𝑦²$$ $$(𝑥-𝑦)³ = 𝑥³ - 3𝑥²𝑦 + 3𝑥𝑦² - 𝑦³$$

Quadratic Formula

$$a𝑥²+bx+c = 0$$ $$⇓$$ $$x= \frac{-b\pm \sqrt{b^2 - 4ac}}{2a}$$

Factorization

We can transform a polynomial into a multiplication of simpler polynomials.

$$∑ aₙ·𝑥ⁿ ⟺ 𝑘 ∏ (𝑥-𝚛ₙ)$$

These terms 𝚛ₙ are called the $Root$ of the polynomial.

We observe that for a 2nd order polynomial

$$x² + bx + c$$

The roots of the square shape are of the form

$$(x-r)(x-s) = x² - (r+s)x + rs$$

Therefore

$$b = ¬(r+s)       c = rs$$

We can easily identify possible basic roots by the factors of the constant $c$.

Polynomial long Division

$P(x) = D(x)·Q(x) + R(x)$

  • $P(x)$ : Dividendo
  • $D(x)$ : Divisor
  • $Q(x)$ : Cociente
  • $R(x)$ : Residuo

Thm of the Residue

If $P(x)$ is divided by $x-c$, then the residue is the value $P(c)$

Thm of the Factor

$c$ is zero of $P$ if and only if $x-c$ is a factor of $P(x)$

Thm of Rational zeros

if the polynomial $P(x)$ has whole coefficients, then all rational zero of it is of the form:

$$\frac{p}{q}$$

where $p$ is a factor of the constant coefficient $a_0$
and $q$ is a factor of the principal coefficient $a_n$

Finding the Zeros:

  1. Make a list of candidates Use the Thm of Rational Zeros
  2. Divide or Check With the Thm of the Factor

Fundamental Thm of Algebra

For every Polynomial function

$$P(x) = a_0 + a_1x + a_2x^2 ⠀.+.⠀ a_nx^n$$

with $n≥1$ has at least one zero $c ∈ ℂ$.

$$P(x) = a(x-c_1)(x - c_2) ⠀.⨯.⠀ (x - c_n) = a∏(x-c_i)$$

There are, then, n solutions $c_i ∈ ℂ$

If $z$ is a solution, the complex conjugate of $z$ is also a solution

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