Normal from tabulated function values

Normal from tabulated function values

Junior College 2
8 marks

The functions \(\mathrm{p}\) and \(\mathrm{q}\) are continuous for \(1\leq x\leq5\). The function \(\mathrm{p}\) is strictly increasing, while \(\mathrm{q}\) is strictly decreasing and \(\mathrm{q}(x)>0\). Selected values are shown below.

\(x\)\(1\)\(2\)\(3\)\(4\)\(5\)
\(\mathrm{p}(x)\)\(-10\)\(-8\)\(-6\)\(-4\)\(5\)
\(\mathrm{q}(x)\)\(5\)\(4\)\(3\)\(2\)\(1\)

Using the information in the table,

  1. Find \(\mathrm{p}\mathrm{q}(2)\).

    [1]
  2. Solve \(\mathrm{p}^{-1}\mathrm{q}(x)=5\).

    [2]

The function \(\mathrm{r}\) is defined by \(\mathrm{r}(x)=\frac{\mathrm{p}(x)}{\mathrm{q}(x)}\).

It is further given that \(\mathrm{p}'(3)=3\) and \(\mathrm{q}'(3)=-1\).

  1. Explain why \(\mathrm{r}^{-1}\) does not exist on the given domain.[2]
  2. Find the equation of the normal to \(y=\mathrm{r}(x)\) at \(x=3\).[3]

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Answer:(a) \(-4\) (b) \(x=1\) (c) \(\mathrm{r}^{-1}\) does not exist on the given domain (d) \(y+2=-3(x-3)\)

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