Sketching the line for a natural exponential law

Sketching the line for a natural exponential law

Secondary 3

The variables \(x\) and \(y\) are related by \(y=8\mathrm{e}^{-0.5x}\).

  1. Sketch the graph of \(\ln y\) against \(x\), marking where it meets both axes and stating its gradient.
  2. Use your line to find the value of \(x\) for which \(y=1\), and explain why the line crosses the horizontal axis there.

Solution:

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Answer:(a) line through \((0,\,2.08)\) and \((4.16,\,0)\), gradient \(-0.5\) (b) \(x=2\ln 8\approx4.16\), because \(\ln 1=0\)

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