Find the value of c in Rolle’s theorem for the function f(x) = x3 – 3x in ![]()
We have-
f(x) = x3-3x
Since a polynomial function is everywhere continuous and
differentiable, therefore f(x) is continuous on [-√3, 0] and
differentiable on [-√3, 0].
Also, f(-√3) = (-√3)3 - 3(-√3) = -3√3 + 3√3 = 0
and, f(0) = (0)3 - 3(0) = 0
∴ f(-√3) = f(0)
Thus, all the three conditions of Rolle's theorem are satisfied.
Thus, there exists c ∈ (-√3, 0) such that f'(c) = 0
Now, f'(x) = 3x2 - 3
∴ f'(x) = 0
⇒ 3x2 - 3 = 0
⇒ 3(x2 - 1) = 0
⇒ x2 - 1 = 0
∴ x = ± 1
Clearly, only -1 lies in the interval (-√3, 0).
Thus, the value of c is -1.
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