Graphing Logarithmic Functions by Walch Education

Graphing Logarithmic Functions by Walch Education
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2014-08-06 02:00
This example demonstrates how to sketch the graphs of the functions f(x) = 2 • log2(x) and g(x) = 2 – log2(x) on a coordinate plane, and describe their asymptotes and symmetry. Key math concepts include logarithmic functions, graphing, and symmetry analysis. GeoGebra commands and objects like If, LaTeX, FractionText, d, c, g, a, e, p, q, r, f, stepMax, hr, layer, stepper, steps, hotspot4, hr0, prevNext, prev, next, b, prevHotspot, nextHotspot, btnInfobox, b1, pic2, b2, b3, b4, b5, b6, b7, btnsOGrandom, randomHotspot, ogHotspot, h, step1, step1_1, step1_{11}, step1_{12}, step1_2 are used in the construction. Suitable for high school students learning about logarithmic functions and their properties.

GeoGebra Commands & Parameters

  1. If(d ≟ 1, " ", LaTeX[d]) → h
  2. LaTeX("\text{Determine function values for } f(1) \text{ and } g(1) \text{ and write the results as ordered pairs.}") → step1
  3. LaTeX("\text{Substitute } x = 1 \text{ into each function and solve.}") → step1_1
  4. LaTeX((((((("f(1) = " * a) * "\cdot \log_") * b) * "(1) = ") * a) * "\cdot 0 = 0")) → step1_{11}
  5. LaTeX(((((((((("g(1) = " * c) * " - ") * h) * " \log_") * b) * "(1) = ") * c) * " - 0 = ") * c)) → step1_{12}
  6. LaTeX("\text{Write each as an ordered pair.}") → step1_2
  7. LaTeX((((((a * "\cdot \log_2\,x = ") * c) * "-") * h) * " \log_2 x")) → step2_1
  8. LaTeX(((e * "\cdot \log_2\,x = ") * c)) → step2_2
  9. LaTeX(((((" \log_2\,x = \frac{" * p) * "}{") * q) * "}")) → step2_3
  10. LaTeX((((((a * "^{\frac{") * p) * "}{") * q) * "}}=x")) → step2_4
  11. FractionText(s) → rt
  12. LaTeX("\text{Find the function value at which the functions are equal.}") → step3
  13. LaTeX((((((((" f(2) = " * a) * "\cdot \log_") * b) * " \; (2) = ") * a) * "\cdot 1=") * f(2))) → step5_3
  14. LaTeX((((((((" g(4) = " * a) * "- \log_") * b) * " \; (4) = ") * a) * "- 2=") * g(4))) → step5_8
  15. LaTeX((((((((" g(2) = " * a) * "- \log_") * b) * " \; (2) = ") * a) * "- 1=") * g(2))) → step5_7
  16. LaTeX((((((((" g(0.5) = " * a) * "- \log_") * b) * " \; (0.5) = ") * a) * "- (-1)=") * g(0.5))) → step5_6
  17. LaTeX((((((((" g(0.25) = " * a) * "- \log_") * b) * " \; (0.25) = ") * a) * "- (-2)=") * g(0.25))) → step5_5
  18. LaTeX((((((((" f(4) = " * a) * "\cdot \log_") * b) * " \; (4) = ") * a) * "\cdot 2=") * f(4))) → step5_4
  19. LaTeX("\text{Find the value(s) of x at which f(x) = g(x). } \cr\text{This will reveal any point(s) of intersection, or solutions, of the system of equations.}") → step2
  20. LaTeX("\text{Set the functions equal to each other.}") → step2_{x1}
  21. LaTeX((("\text{Add } " * h) * " \log_2 x \text{ to both sides.}")) → step2_{x2}
  22. LaTeX((("\text{Divide both sides by }" * q) * ".")) → step2_{x3}
  23. LaTeX("\text{Simplify.}") → step2_{x4}
  24. LaTeX(((((("\text{Substitute the approximate value of x from step 2 into each function.} \cr\ \cr \cr\ \cr\ f(" * r) * ")\approx g(") * r) * ") \approx ") * s)) → step3_1
  25. LaTeX("\text{Write the approximate point at which the functions intersect.}") → step4
  26. LaTeX("\text{Write the additional points. Make sure to keep the points with the correct function.}") → step6
  27. LaTeX("\text{For f(x): As x approaches positive infinity, f(x) approaches positive infinity. } \cr\text{As x approaches 0, f(x) approaches negative infinity.}") → step8_2
  28. LaTeX("\text{For g(x): As x approaches positive infinity, g(x) approaches negative infinity. } \cr\text{As x approaches 0, g(x) approaches positive infinity.}") → step8_3
  29. LaTeX((((((((((("\text{Sketch the graphs of the functions } f(x) = " * a) * "\cdot \log_") * b) * "x \text{ and } g(x) = ") * c) * "-") * h) * "\log_") * b) * "x. \cr\text{Describe the end behavior of each function.}")) → Problem
  30. LaTeX("f(1) = 0: (1,0)") → step1_{21}
  31. LaTeX((((("g(1) = " * c) * ": (1,") * c) * ")")) → step1_{22}
  32. LaTeX((("\text{Using a calculator, x} \approx" * round((10 * a^(p / q))) / 10) * ".")) → step2_5
  33. LaTeX((((("\text{The intersection point is approximately } (" * r) * ",\, ") * s) * ").")) → step4_1
  34. LaTeX("\text{Determine additional points for sketching the graph of each function.} \cr\text{Choose values of x that can be evaluated easily. }") → step5
  35. LaTeX(" \text{Solve f(x) for x = 0.25, 0.5, 2, and 4.}") → step5_{f}
  36. LaTeX(" \text{Solve g(x) for x = 0.25, 0.5, 2, and 4.}") → step5_{g}
  37. LaTeX((((((((" f(0.25) = " * a) * "\cdot \log_") * b) * " \; (0.25) = ") * a) * "\cdot -2=") * f(0.25))) → step5_1
  38. LaTeX((((((((" f(0.5) = " * a) * "\cdot \log_") * b) * " \; (0.5) = ") * a) * "\cdot -1=") * f(0.5))) → step5_2
  39. LaTeX("\text{Plot the graphs.}") → step7
  40. LaTeX("\text{It is useful to know the limits of function values as the values go} \cr\text{beyond the finite values used for a sketch of a graph.}") → step8_1
  41. LaTeX(((((((((" \text{For f(x): A = }(0.25, " * f(0.25)) * ")\text{, B = }(0.5, ") * f(0.5)) * ")\text{, C = }(2, ") * f(2)) * ")\text{, and D = }(4,") * f(4)) * ") ")) → step6_1
  42. LaTeX(((((((((" \text{For g(x): E = }(0.25, " * g(0.25)) * ")\text{, F = }(0.5, ") * g(0.5)) * ")\text{, G = }(2, ") * g(2)) * ")\text{, and H = }(4,") * g(4)) * ") ")) → step6_2
  43. LaTeX("\text{Describe what happens to the function values as x becomes very large } \cr\text{and as x approaches 0.}") → step8