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1991 WAEC Mathematics Theory Using a scale of 2cm to 1 unit on the x- axis and 1cm to...

Mathematics
WAEC 1991

Using a scale of 2cm to 1 unit on the x- axis and 1cm to 1 unit on the y- axis, draw on the same axes the graphs of \(y = 3 + 2x - x^{2}; y = 2x - 3\) for \(-3 \leq x \leq 4\). Using your graph:

(i) solve the equation \(6 - x^{2} = 0\);

(ii) find the maximum value of \(3 + 2x - x^{2}\);

(iii) find the range of x for which \(3 + 2x - x^{2} \leq 1\), expressing all your answers correct to one decimal place.

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Explanation

\(y = 3 + 2x - x^{2}\) and \(y = 2x - 3\)

Table of values for the equation for \(-3 \leq x \leq 4\)

x -3 -2 -1 0 1 2 3 4
\(y = 3 + 2x - x^{2}\) -12 -5 0 3 4 3 0 5
\(y = 2x - 3\) -9 -7 -5 -3 -1 1 3 5

(i) \(6 - x^{2} = 0\)

\(6 - 3 + 2x - x^{2} = 2x - 3\)

\(3 + 2x - x^{2} = 2x - 3\)

\(\therefore y = 2x - 3\)

Read the point where the two equations intersect on the graph.

x = -2.6 and x = 2.5.

(ii) Maximum value of \(3 + 2x - x^{2}\) is at y = 4.

(iii) Range for which \(3 + 2x - x^{2} \leq 1\) is represented by the shaded portion in the graph.


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