(a) Express \(f(x) = -3x^2 + 12x + 2\) in the form \(-3(x-a)^2 + b\), where \(a\) and \(b\) are constants.
The result of translating the graph of \(y = f(x)\) by \(\begin{pmatrix} -3 \\ 1 \end{pmatrix}\) is the graph of \(y = g(x)\).
(e) Express \(g(x)\) in the form \(px^2 + qx + r\), where \(p, q,\) and \(r\) are constants.
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Solution
(a) To express \(f(x) = -3x^2 + 12x + 2\) in the form \(-3(x-a)^2 + b\), we complete the square:
Start with \(-3(x^2 - 4x) + 2\).
Complete the square for \(x^2 - 4x\):
\(x^2 - 4x = (x-2)^2 - 4\).
Substitute back:
\(-3((x-2)^2 - 4) + 2 = -3(x-2)^2 + 12 + 2 = -3(x-2)^2 + 14\).
Thus, \(a = 2\) and \(b = 14\).
(e) Given the translation vector \(\begin{pmatrix} -3 \\ 1 \end{pmatrix}\), the function \(g(x)\) is obtained by substituting \(x+3\) into \(f(x)\) and adding 1:
\(g(x) = -3((x+3)-2)^2 + 14 + 1\).
Simplify:
\(g(x) = -3(x+1)^2 + 15\).
Expand \(-3(x+1)^2\):
\(-3(x^2 + 2x + 1) = -3x^2 - 6x - 3\).
Thus, \(g(x) = -3x^2 - 6x - 3 + 15 = -3x^2 - 6x + 12\).
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