Completing the Square when \(a\ne 1\)

Completing the Square when \(a\ne 1\)

Secondary 3

Express \(y=4{{x}^{2}}-8x-5\) in the form \(y=a{{(x-h)}^{2}}+k\), where \(a\), \(h\) and \(k\) are constants. Hence, state

  1. Find the maximum or minimum value of the graph
  2. The value of \(x\) at which the maximum or minimum occurs
  3. Hence, sketch the curve for \(y=4{{x}^{2}}-8x-5\), indicating clearly the turning points and intercepts on the axes.

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Answer:\(y=4(x-1)^2-9\) (i) Minimum \(-9\) (ii) \(x=1\) (iii) \(x=-\frac12,\frac52\); \(y\)-intercept \((0,-5)\)

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