If y = x³ - x² - x + 6, find the values of x at the turning point.

Correct Answer is : 1,−131, -1/31,−31

Correct Answer is : 1,−131, -1/31,−31

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WAEC Further Mathematics 2012 Paper

Question : 13

Total: 40

y = x^{3} - x^{2} - x + 6

, find the values of x at the turning point.

Solution:

At turning point, $\frac{dy}{dx} = 0$ .

Given $x^{3} - x^{2} - x + 6$

$\frac{dy}{dx} = 3x^{2} - 2x - 1 = 0$

$3x^{2} - 3x + x - 1 = 0 \implies (3x + 1)(x - 1) = 0$

$x = \frac{-1}{3}, 1$

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