Question
Verify Rolle's theorem for the following function on the indicated intervals
f(x) = x2 - 8x + 12 on [2, 6]

Answer

Given:

f(x) = x2 - 8x + 12

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

So, being a polynomial function f(x) is continuous and derivable on [2, 6].

f(2) = (2)2 - 8(2) + 12 = 4 - 16 + 12 = 0

f(6) = (6)2 - 8(6) + 12 = 36 - 48 + 12 = 0

$\therefore$ f(2) = f(6) = 0

Thus, all the conditions of rolle's theorem are satisfied.

Now, we have to show that there exist $\text{c}\in(2, 6)$ such that f'(c) = 0

We have

f(x) = x2 - 8x + 12

⇒ f'(x) = 2x - 8

$\therefore$ f'(x) = 0

⇒ 2x - 8 = 0

⇒ x = 4

Thus, $\text{c}=4\in(2,6)$ such that f'(c) = 0

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