Graphing Logarithmic Functions by Walch Education
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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
If(d ≟ 1, " ", LaTeX[d]) → hLaTeX("\text{Determine function values for } f(1) \text{ and } g(1) \text{ and write the results as ordered pairs.}") → step1LaTeX("\text{Substitute } x = 1 \text{ into each function and solve.}") → step1_1LaTeX((((((("f(1) = " * a) * "\cdot \log_") * b) * "(1) = ") * a) * "\cdot 0 = 0")) → step1_{11}LaTeX(((((((((("g(1) = " * c) * " - ") * h) * " \log_") * b) * "(1) = ") * c) * " - 0 = ") * c)) → step1_{12}LaTeX("\text{Write each as an ordered pair.}") → step1_2LaTeX((((((a * "\cdot \log_2\,x = ") * c) * "-") * h) * " \log_2 x")) → step2_1LaTeX(((e * "\cdot \log_2\,x = ") * c)) → step2_2LaTeX(((((" \log_2\,x = \frac{" * p) * "}{") * q) * "}")) → step2_3LaTeX((((((a * "^{\frac{") * p) * "}{") * q) * "}}=x")) → step2_4FractionText(s) → rtLaTeX("\text{Find the function value at which the functions are equal.}") → step3LaTeX((((((((" f(2) = " * a) * "\cdot \log_") * b) * " \; (2) = ") * a) * "\cdot 1=") * f(2))) → step5_3LaTeX((((((((" g(4) = " * a) * "- \log_") * b) * " \; (4) = ") * a) * "- 2=") * g(4))) → step5_8LaTeX((((((((" g(2) = " * a) * "- \log_") * b) * " \; (2) = ") * a) * "- 1=") * g(2))) → step5_7LaTeX((((((((" g(0.5) = " * a) * "- \log_") * b) * " \; (0.5) = ") * a) * "- (-1)=") * g(0.5))) → step5_6LaTeX((((((((" g(0.25) = " * a) * "- \log_") * b) * " \; (0.25) = ") * a) * "- (-2)=") * g(0.25))) → step5_5LaTeX((((((((" f(4) = " * a) * "\cdot \log_") * b) * " \; (4) = ") * a) * "\cdot 2=") * f(4))) → step5_4LaTeX("\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.}") → step2LaTeX("\text{Set the functions equal to each other.}") → step2_{x1}LaTeX((("\text{Add } " * h) * " \log_2 x \text{ to both sides.}")) → step2_{x2}LaTeX((("\text{Divide both sides by }" * q) * ".")) → step2_{x3}LaTeX("\text{Simplify.}") → step2_{x4}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_1LaTeX("\text{Write the approximate point at which the functions intersect.}") → step4LaTeX("\text{Write the additional points. Make sure to keep the points with the correct function.}") → step6LaTeX("\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_2LaTeX("\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_3LaTeX((((((((((("\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.}")) → ProblemLaTeX("f(1) = 0: (1,0)") → step1_{21}LaTeX((((("g(1) = " * c) * ": (1,") * c) * ")")) → step1_{22}LaTeX((("\text{Using a calculator, x} \approx" * round((10 * a^(p / q))) / 10) * ".")) → step2_5LaTeX((((("\text{The intersection point is approximately } (" * r) * ",\, ") * s) * ").")) → step4_1LaTeX("\text{Determine additional points for sketching the graph of each function.} \cr\text{Choose values of x that can be evaluated easily. }") → step5LaTeX(" \text{Solve f(x) for x = 0.25, 0.5, 2, and 4.}") → step5_{f}LaTeX(" \text{Solve g(x) for x = 0.25, 0.5, 2, and 4.}") → step5_{g}LaTeX((((((((" f(0.25) = " * a) * "\cdot \log_") * b) * " \; (0.25) = ") * a) * "\cdot -2=") * f(0.25))) → step5_1LaTeX((((((((" f(0.5) = " * a) * "\cdot \log_") * b) * " \; (0.5) = ") * a) * "\cdot -1=") * f(0.5))) → step5_2LaTeX("\text{Plot the graphs.}") → step7LaTeX("\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_1LaTeX(((((((((" \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_1LaTeX(((((((((" \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_2LaTeX("\text{Describe what happens to the function values as x becomes very large } \cr\text{and as x approaches 0.}") → step8