Question
Verify Rolle's theorem for the following function on the indicated intervals

f(x) = x(x - 1)2 on [0, 1]

Answer

Given

f(x) = x(x - 1)2

⇒ f(x) = x(x2 - 2x + 1)

$\therefore$ f(x) = (x3 - 2x2 + x)

We know that a polynominal function is everywhere derivable and hence continuous.

So, being a polynomial function, f(x) is continuous and derivable on [0, 1]

Also,

f(0) = f(1) = 0

Thus, all the continuous of Solids theorem are satisfied.

Now, we have to show that there exists $\text{c}\in(0,1)$ such that f'(c) = 0.

We have

f(x) = x3 - 2x2 + x

⇒ f'(x) = 3x2 - 4x + 1

$\therefore$ f'(x) = 0 ⇒ 3x- 4x + 1 = 0

⇒ 3x- 3x - x + 1 = 0

⇒ 3x(x - 1) - 1(x - 1) = 0

⇒ (x - 1)(3x - 1) = 0

$\Rightarrow\text{x}=1,\frac{1}{3}$

Thus, $\text{c}=\frac{1}{3}\in(0,1)$ such that f'(c) = 0.

Hence, Rolle's theorem is verified.

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