Basic Classes of Functions: Fresh Take

  • Recognize the degree of a polynomial, find the roots of quadratic polynomials, and describe the graphs of basic odd and even polynomial functions
  • Graph a piecewise-defined function
  • Explain the difference between algebraic and transcendental functions
  • Sketch the graph of a function that has been shifted, stretched, or reflected from its initial graph position

Polynomial Functions

The Main Idea 

  • A polynomial function is of the form [latex]f(x) = a₁xⁿ + a₂xⁿ⁻¹ + ... + aₙ₋₁x + aₙ,[/latex] where [latex]n[/latex] is a non-negative integer.
  • Key Terms:
    • Degree: The highest power of [latex]x[/latex] in the polynomial
    • Leading Term: The term with the highest degree
    • Leading Coefficient: The coefficient of the leading term
  • Types of Polynomials:
    • Linear: Degree [latex]1[/latex] (e.g., [latex]f(x) = mx + b[/latex])
    • Quadratic: Degree [latex]2[/latex] (e.g., [latex]f(x) = ax² + bx + c[/latex])
    • Cubic: Degree [latex]3[/latex]
    • Higher degrees: Quartic ([latex]4[/latex]), Quintic ([latex]5[/latex]), etc.
  • The zero function [latex]f(x) = 0[/latex] is considered a polynomial of degree [latex]0[/latex].

Identify the degree, leading term, and leading coefficient for each of the following functions:

  1. [latex]h(y) = 2y⁴ - 3y² + 5y - 7[/latex]
  2. [latex]k(s) = -0.5s³ + 2s - 1[/latex]
  3. [latex]m(w) = w⁵ + 3w⁴ - 2w² + w[/latex]

Zeros of Polynomial Functions

The Main Idea 

  • For quadratic functions [latex]f(x) = ax² + bx + c[/latex], zeros can be found using:
    • Factoring (if possible)
    • The quadratic formula: [latex]x = \dfrac{-b ± \sqrt{(b² - 4ac)}}{ (2a)}[/latex]
  • The discriminant [latex](b² - 4ac)[/latex] determines the nature of quadratic solutions:
    • Positive: Two distinct real roots
    • Zero: One real root (double root)
    • Negative: No real roots
  • Higher-degree polynomials may have more complex methods for finding zeros.

Find the zeros of the quadratic function [latex]g(x) = 2x² + 5x - 3[/latex].

Graphs of Polynomial Functions Basics

The Main Idea 

  • The degree of a polynomial greatly influences its graph’s shape.
  • Even-degree polynomials:
    • Both ends of the graph point in the same direction (up or down)
    • Similar to a parabola, but may be flatter near the origin
  • Odd-degree polynomials:
    • Ends of the graph point in opposite directions
    • One end goes up, the other goes down
  • The sign of the leading coefficient determines the direction of the graph’s ends:
    • Positive leading coefficient: right end goes up
    • Negative leading coefficient: right end goes down
  • As the degree increases, graphs tend to flatten near the origin and become steeper away from it.

Describe the end behavior and basic shape of the graph for the polynomial function:

[latex]f(x) = -2x⁵ + 3x⁴ - x² + 7[/latex]

Piecewise-Defined Functions

The Main Idea 

  • A piecewise-defined function uses different formulas for different parts of its domain.
  • Each piece of the function has its own subdomain, which together form the function’s complete domain.
  • Piecewise functions may be continuous or discontinuous, depending on how the pieces connect.
  • Each piece is graphed separately within its specified domain, paying special attention to the transition points.

Sketch a graph of the function

[latex]f(x)=\begin{cases} 2-x, & x \le 2 \\ x+2, & x>2 \end{cases}[/latex]

The cost of mailing a letter is a function of the weight of the letter. Suppose the cost of mailing a letter is [latex]49\text{¢}[/latex] for the first ounce and [latex]21\text{¢}[/latex] for each additional ounce. Write a piecewise-defined function describing the cost [latex]C[/latex] as a function of the weight [latex]x[/latex] for [latex]0 < x \le 3[/latex], where [latex]C[/latex] is measured in cents and [latex]x[/latex] is measured in ounces.

Algebraic Functions and Transcendental Functions

The Main Idea 

  • Algebraic Functions:
    • Involve addition, subtraction, multiplication, division, rational powers, and roots
    • Include polynomial, rational, and root functions
    • Examples: [latex]f(x) = x³ + 2x - 1, g(x) = \frac{(x² + 1) }{ (x - 2)}, h(x) = \sqrt{(x + 3)}[/latex]
  • Transcendental Functions:
    • Cannot be expressed using a finite number of algebraic operations
    • Main types: trigonometric, exponential, and logarithmic functions
    • Examples: [latex]sin(x), e^x, log₂(x)[/latex]

Is [latex]f(x)=\dfrac{x}{2}[/latex] an algebraic or a transcendental function?

Classify the following functions as algebraic or transcendental, and identify their specific type if possible:

  1. [latex]f(x) = \frac{(x⁴ + 2x² - 5)}{ (x - 1)}[/latex]
  2. [latex]g(x) = sin(x²) + cos(x)[/latex]
  3. [latex]h(x) = \sqrt[3]{(x² + 1)} + log₃(x)[/latex]
  4. [latex]k(x) = \frac{(2^x + 3^x)}{x}[/latex]

Transformations of Functions 

The Main Idea 

  • Vertical Shift: [latex]f(x) ± c[/latex]
    • [latex]+c[/latex] shifts up, [latex]-c[/latex] shifts down
    • Does not change shape of graph
  • Horizontal Shift: [latex]f(x ± c)[/latex]
    • [latex]-c[/latex] shifts right, [latex]+c[/latex] shifts left
    • Does not change shape of graph
  • Vertical Scaling: [latex]cf(x)[/latex]
    • [latex]|c| > 1[/latex] stretches vertically, [latex]0 < |c| < 1[/latex] compresses vertically
    • Changes height of graph
  • Horizontal Scaling: [latex]f(cx)[/latex]
    • [latex]0 < |c| < 1[/latex]stretches horizontally, [latex]|c| > 1[/latex] compresses horizontally
    • Changes width of graph
  • Reflections:
    • [latex]-f(x)[/latex] reflects over [latex]x[/latex]-axis
    • [latex]f(-x)[/latex] reflects over [latex]y[/latex]-axis
  • Multiple Transformations: [latex]y = cf(a(x + b)) + d[/latex]
    • Apply in order: horizontal shift, horizontal scaling, vertical scaling, vertical shift

Transform the following function which has the base tool-kit function [latex]f(x) = \sqrt{x}[/latex]:

[latex]g(x) = 2\sqrt{(x - 1)} + 3[/latex]