CCGPS AA 5.2.3 Example 3: Write an Equation to Describe the Graphed Function

CCGPS AA 5.2.3 Example 3: Write an Equation to Describe the Graphed Function
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2014-05-13 21:29
In collections CCGPS AA Unit 5 Lesson 2
This example demonstrates how to write an equation that describes a given function graph, with a focus on the tangent function. The core mathematical concepts include the period, amplitude, phase shift, and vertical shift of the tangent function, and how to extract these parameters from the graph to construct the function expression. In terms of construction, the summary shows the use of GeoGebra commands such as LaTeX, Segment, If, Vector, Min, Max, and TableText, along with multiple sliders (stepMax, stepper, steps, counter) and parameters (a, b, cmult, d, f, period, c, amplitude) to dynamically adjust function parameters. Text objects (text1, cosshiftText, sincmult, sinshiftText, etc.) are used to display the equation derivation process. This example is suitable for high school or pre-university students learning trigonometric function transformations, and can also be used by teachers for classroom demonstrations on how to reverse-engineer a function equation from its graph, fostering visual-symbolic reasoning and reverse thinking.

GeoGebra Commands & Parameters

  1. LaTeX(steps) → counter
  2. Segment(A, B) → period
  3. Segment(C, A) → amplitude
  4. LaTeX("\text{Choose to use either the sine or cosine form.}") → text1
  5. If(cmult > 0, LaTeX["\text{ to the right}"], If[cmult < 0, LaTeX["\text{ to the left}"], ""]) → cosshiftText
  6. If(sincmult > 0, LaTeX["\text{ to the right}"], If[sincmult < 0, LaTeX["\text{ to the left}"], ""]) → sinshiftText
  7. LaTeX("\text{Determine the value of a.}") → text7
  8. LaTeX("\text{Determine the value of b.}") → text10
  9. LaTeX("\text{Determine the value of c.}") → text16
  10. LaTeX("\text{The variable c gives the horizontal shift.}") → text17
  11. Vector(E, A) → u
  12. Vector(F, D) → v
  13. LaTeX("\text{Determine the value of d.}") → text24
  14. LaTeX("\text{The variable d gives the vertical shift.}") → text25
  15. If(d > 0, " up", If[d < 0, " down", ""]) → vertshiftText
  16. If(d > 0, "+", If[d < 0, "-", ""]) → vertshiftSign
  17. LaTeX((("\text{The value of d, the vertical shift, is " * d) * ".}")) → text27
  18. Vector(((3 * period / 8), 0), ((3 * period / 8), d)) → w
  19. LaTeX(("f(x)=" * f)) → text32
  20. LaTeX((((((((("f(x)=(" * a) * ")\cos\left[(") * b) * ")(x-") * FractionText[cmult]) * "\pi)\right]+(") * d) * ")")) → text31
  21. LaTeX((((((((("f(x)=(" * a) * ")\sin\left[(") * b) * ")(x-") * FractionText[cmult - 0.25]) * "\pi)\right]+(") * d) * ")")) → text35
  22. LaTeX(("f(x)=" * g)) → text36
  23. Min(0 - a, d - (2 * a)) → ymin
  24. Max(0 + a, d + (2 * a)) → ymax
  25. LaTeX((((((FractionText[cmult + 2 / b] * "\pi-") * FractionText[cmult]) * "\pi=") * FractionText[2 / b]) * "\pi")) → text13
  26. LaTeX("\text{Move the slider to solve the problem.}") → text0
  27. LaTeX("\text{This periodic function can be described by a sine function or a cosine function. }\cr\text{Either function will work.}") → text2
  28. LaTeX((((((("\text{There is an identifiable rising midpoint at x = }" * FractionText[sincmult]) * "\pi. \cr\text{Thus, this function can be described as a sine function }\cr\text{that has been shifted }") * FractionText[abs(sincmult)]) * "\pi\text{ units}") * sinshiftText) * ".")) → text6
  29. LaTeX((((((("\text{There is an identifiable maximum at x = }" * FractionText[cmult]) * "\pi. \cr\text{Thus, this function can be described as a cosine function }\cr\text{that has been shifted } ") * FractionText[abs(cmult)]) * "\pi\text{ units}") * cosshiftText) * ".")) → text4
  30. LaTeX("\text{The variable a is the amplitude, or how far the function rises above its midline.}") → text8
  31. LaTeX("\text{The period (the length of one cycle of the curve) is equal to }\frac{2\pi}{b}.") → text11
  32. LaTeX((((("\text{One cycle of this curve starts at x =}" * FractionText[cmult]) * "\pi\text{ and ends at x = }") * FractionText[cmult + 2 / b]) * "\pi. \cr\text{Subtract to find the length of one cycle of the curve.}")) → text12
  33. LaTeX((("\text{The period of the function is }" * FractionText[2 / b]) * "\pi. \cr\text{Substitute this value into the formula for the period of the}\cr\text{function and solve for b.}")) → text14
  34. LaTeX("\text{The value of the horizontal shift depends on whether the curve}\cr\text{is viewed as a cosine function or as a sine function.}") → text18
  35. LaTeX("\text{In either case, shifts to the right are designated as positive }\cr\text{and shifts to the left are designated as negative.}") → text19
  36. LaTeX("\text{Substitute a, b, c, and d into the general form of the cosine or sine function.}") → text28
  37. LaTeX("\text{Substitute the known values into the general form of the }\cr\text{cosine function and simplify.}") → text29
  38. LaTeX("\text{Use the buttons below to return to the original problem or}\cr\text{randomly generate a similar practice problem.}") → text37
  39. LaTeX((((((("\text{The midline is y = }" * d) * "\text{, and the function rises }") * a) * " \text{ unit(s) above its midline. }\cr\text{Therefore, the value of a, the amplitude, is }") * a) * ".")) → text9
  40. TableText({{LaTeX["\text{period}=\frac{2\pi}{b}"], LaTeX["\text{Formula for the period}"]}, {LaTeX[(FractionText[2 / b] * "\pi=\frac{2\pi}{b}")], LaTeX["\text{Substitute for the period.}"]}, {LaTeX[(("\left(" * FractionText[2 / b]) * "\pi\right)b=2\pi")], LaTeX["\text{Multiply both sides by b.}"]}, {LaTeX[(("b=\frac{2\pi}{" * FractionText[2 / b]) * "\pi}")], LaTeX["\text{Divide both sides by the period.}"]}, {LaTeX[("b=" * b)], LaTeX["\text{Simplify.}"]}}) → text15
  41. LaTeX("\text{As a cosine function:}") → text20
  42. LaTeX((("\text{}c=" * FractionText[cmult]) * "\pi")) → text21
  43. LaTeX("\text{As a sine function:}") → text22
  44. LaTeX((("\text{}c=" * FractionText[cmult - 0.25]) * "\pi")) → text23
  45. LaTeX((((((((((("\text{The midline is y = }" * d) * "\text{; thus, the function has been shifted") * vertshiftText) * " ") * abs(d)) * " units (") * vertshiftSign) * "") * d) * ").}")) → text26
  46. LaTeX("\text{f(x) = a cos [b(x – c)] + d}") → text30
  47. LaTeX("\text{Or, substitute the known values into the general form of the }\cr\text{sine function and simplify.}") → text33
  48. LaTeX("\text{f(x) = a sin [b(x – c)] + d}") → text34
  49. LaTeX("\text{For cosine form:}") → text3
  50. LaTeX("\text{For sine form:}") → text5

AI Drawing Prompt Reference

Draw the graph of a tangent function and show how to extract the period, amplitude, phase shift, and vertical shift parameters from the graph to construct the function expression. Use sliders to dynamically adjust these parameters and display the derivation process and the final function expression. The image should include multiple text objects explaining the meaning and derivation steps of each parameter.
The prompt above was compiled from the original drawing commands and is for reference only.