What will be the range of the function f(x) = 2x3 – 9x2 – 24x + 5 which increases with x?
What will be the range of the function f(x) = 2x3 – 9x2 – 24x + 5 which increases with x? Correct Answer x > 4 or x < -1
Since f(x) = 2x3 – 9x2 – 24x + 5 Therefore, f’(x) = 6x2 – 18x + 24 = 6(x – 4)(x + 1) If x > 4, then, x – 4 > 0 and x + 1 > 0 Thus, (x – 4)(x + 1) > 0 i.e., f’(x) > 0, when x > 4 Again, if x < -1, then, x – 4 < 0 and x + 1 < 0 So, from here, (x – 4)(x + 1) > 0 i.e., f’(x) > 0, when x < -1 Hence, f’(x) > 0, when x > 4 Or x < -1 Therefore, f(x) increases with x when, x > 4 or x < -1
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Feb 20, 2025