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June 2022 p13 q4
666
(a) The curve with equation \(y = x^2 + 2x - 5\) is translated by \(\begin{pmatrix} -1 \\ 3 \end{pmatrix}\). Find the equation of the translated curve, giving your answer in the form \(y = ax^2 + bx + c\).
(b) The curve with equation \(y = x^2 + 2x - 5\) is transformed to a curve with equation \(y = 4x^2 + 4x - 5\). Describe fully the single transformation that has been applied.
Solution
(a) To translate the curve \(y = x^2 + 2x - 5\) by \(\begin{pmatrix} -1 \\ 3 \end{pmatrix}\), we substitute \(x + 1\) for \(x\) in the equation and add 3 to the result:
\(y = (x+1)^2 + 2(x+1) - 5 + 3\)
Expanding, we get:
\(y = (x^2 + 2x + 1) + (2x + 2) - 5 + 3\)
\(y = x^2 + 4x + 1\)
(b) The transformation from \(y = x^2 + 2x - 5\) to \(y = 4x^2 + 4x - 5\) is a horizontal stretch. The coefficient of \(x^2\) changes from 1 to 4, indicating a stretch in the x-direction by a factor of \(\frac{1}{2}\), keeping the y-axis invariant.