Find the interval(s) on which $f(x) = - 2 x^{2} - 10 x + 5$ is strictly decreasing.

(-\infty, - \frac{5}{2})

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(- \frac{5}{2}, \infty)

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(-\infty, \frac{5}{2})

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\mathbb{R}

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Show the answer and explanation

CorrectNot quiteAnswer B

Correct answer: B

Worth noting

For $a < 0$ the parabola opens down, so it rises first and falls after $x = - \frac{5}{2}$ .

Ten questions from Increasing & Decreasing Functions, at your own pace.

Ten questions from Increasing & Decreasing Functions, at your own pace.

Find the interval(s) on which f(x)=−2x2−10x+5f(x) = - 2 x^{2} - 10 x + 5f(x)=−2x2−10x+5 is strictly decreasing.