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Inverse Graphs

The natural logarithm undoes the exponential function. Their graphs are reflections of each other across the line y = x.

In the picture

  1. Steep rising curve: rises from lower left and continues upward to the right
  2. Slow rising curve: hugs the vertical axis below the origin and rises slowly to the right
  3. Dashed diagonal line: passes through the origin at forty-five degrees
  4. Point on the vertical axis: one unit above the origin
  5. Point on the horizontal axis: one unit right of the origin

Examples

  • Compound interest grows exponentially, and a natural logarithm can estimate how long it takes for an investment to reach a target.
  • A cooling drink loses its temperature difference exponentially, and a natural logarithm can estimate the elapsed cooling time.

Quiz: Inverse Graphs (Age 18)

  1. What is the relationship between the natural logarithm and the exponential function?

    • They are unrelated
    • They undo each other
    • They are both straight lines
  2. Across which line are the graphs of the natural logarithm and the exponential function mirror images?

    • The line x = 0
    • The line y = x
    • The line y = 0
  3. What does the natural logarithm undo?

    • The quadratic function
    • The exponential function
    • The sine function

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Maths, Age 18