Verify that the function satisfies the three hypotheses of Rolle’s Theorem on the given interval. Then find all numbers c that satisfy the conclusion of Rolle’s Theorem. f(x)=5 - 12x + 3x2, [1, 3]
Solution:
Given, the function is f(x) = 5 - 12x + 3x2
We have to find all numbers that satisfy the conclusion of Rolle’s theorem in the interval [1, 3].
Rolle’s theorem states that if a function f is continuous on the closed interval [a, b] and differentiable on the open interval (a, b) such that f(a) = f(b), then f′(x) = 0 for some x with a ≤ x ≤ b.
All polynomials are continuous and differentiable on the set of real numbers.
In the given interval, the function becomes
f(1) = 5 - 12(1) + 3(1)2
= 5 - 12 + 3
= 8 - 12
= -4
f(3) = 5 - 12(3) + 3(3)2
= 5 - 36 + 3(9)
= 5 - 36 + 27
= 32 - 36
= -4
This implies that there is c in the interval [1, 3], such that f’(c) = 0.
On differentiating,
f’(c) = 0 - 12 + 6x
f’(c) = 6x - 12
Solving for f’(c) = 0 for c,
6c - 12 = 0
6c = 12
c = 12/6
c = 2
Therefore, the value of c is 2.
Verify that the function satisfies the three hypotheses of Rolle’s Theorem on the given interval. Then find all numbers c that satisfy the conclusion of Rolle’s Theorem. f(x)=5 - 12x + 3x2, [1, 3]
Summary:
On verifying the function satisfies the three hypotheses of Rolle’s Theorem on the given interval, then all numbers c that satisfy the conclusion of Rolle’s Theorem. f(x)=5 - 12x + 3x2, [1, 3] is 2.
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