Quadratic Graphs

Quadratic Graphs

Secondary 3

Answer the whole of this question on a single sheet of graph paper.

The variables \(x\) and \(y\) are connected by the equation

\(y=2{{x}^{2}}-x-5\)

Some corresponding values of \(x\) and \(y\) are given in the table below.

\(x\)

\(-2\)

\(-1\)

\(0\)

\(1\)

\(2\)

\(3\)

\(y\)

\(5\)

\(a\)

\(-5\)

\(-4\)

\(1\)

\(10\)

  1. Calculate the value of \(a\).
  2. Using a scale of 2 cm to 1 unit, draw a horizontal \(x\)-axis for \(-2\le x\le 3\) and a scale of 1 cm to 1 unit, draw a vertical \(y\)-axis \(-5\le y\le 10\).
    On your axes, plot the points given in the table and join them smoothly.
  3. Use your graph to find the solutions of the equation \(2{{x}^{2}}-x-5=0\).

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Answer:(a) a = -2; (c) x = -1.35 or 1.85.

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