Quadratic Functions, Equations and Inequalities - Solving Quadratic Equations Graphically

Quadratic Functions, Equations and Inequalities - Solving Quadratic Equations Graphically

IP 2

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

The table below gives some \(x\) and \(y\) values of the equation \(y=-{{x}^{2}}-2x+5\).

\(x\)

\(-4\)

\(-3\)

\(-2\)

\(-1\)

\(0\)

\(1\)

\(2\)

\(3\)

\(y\)

\(-3\)

\(2\)

\(5\)

\(6\)

\(5\)

\(2\)

\(-3\)

\(a\)

  1. Find the value of \(a\).
  2. Taking \(2\) cm to represent \(1\) unit on the \(x\)-axis and \(1\) cm to represent \(1\) unit on the \(y\)-axis, draw the graph of \(y=-{{x}^{2}}-2x+5\) for \(-4\le x\le 3\).
  3. Use your graph to find
    1. the coordinates of the maximum point,
    2. the value of \(y\) when \(x=-1.5\),
    3. the values of \(x\) when \(y=4\),
    4. the equation of the line of symmetry.
  4. By drawing a suitable line, find the solutions to the equations
    1. \(-{{x}^{2}}-2x-3=0\),
    2. \(-{{x}^{2}}-x+7=0\).

Solution:

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Answer:(a) \(a=-10\) (b) Graph shown in working (c)(i) \((-1,6)\) (ii) \(y\approx5.8\) (iii) \(x\approx-2.41\) or \(0.41\) (iv) \(x=-1\) (d)(i) No real solutions (ii) \(x\approx-3.19\) or \(2.19\)

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