The equation of a curve C is \(y = 2x^2 - 8x + 9\) and the equation of a line L is \(x + y = 3\).
(i) Find the x-coordinates of the points of intersection of L and C.
(ii) Show that one of these points is also the stationary point of C.
Solution
(i) To find the points of intersection, substitute \(y = 3 - x\) from the line equation into the curve equation:
\(2x^2 - 8x + 9 = 3 - x\)
Rearrange to form a quadratic equation:
\(2x^2 - 7x + 6 = 0\)
Factorize:
\((2x - 3)(x - 2) = 0\)
Thus, \(x = 2\) or \(x = \frac{3}{2}\).
(ii) To find the stationary point of C, differentiate \(y = 2x^2 - 8x + 9\):
\(\frac{dy}{dx} = 4x - 8\)
Set \(\frac{dy}{dx} = 0\):
\(4x - 8 = 0\)
\(x = 2\)
Therefore, \(x = 2\) is a stationary point of C.
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