Monday, November 18, 2013

At what x value on the interval [-2,3] does the graph of f(x)=x^2+2x-1 satisfy the mean value theorem?

The Mean Value Theorem states that if a function is
continuous and differentiable over the closed interval [a,b], then there is a point c,
that belongs to [a,b], such that:


f'(c) = [f(b) -
f(a)]/(b-a)


To calculate f'(c), we'll have to differentiate
the function f(x).


f'(x) =
(x^2+2x-1)'


f'(x) = 2x +
2


Now, we'll substitute x by
c:


f'(c) = 2c + 2


From the
mean value theorem, we'll get:


f'(c) = [f(3) - f(-2)]/(3 +
2)


We'll calculate f(3):


f(3)
= 3^2+2*3-1


f(3) =9+6-1


f(3)
=14


We'll calculate
f(-2):


f(-2) =
(-2)^2+2*(-2)-1


f(-2) = 4 - 4 -
1


We'll eliminate like
terms:


f(-2) = -1


f'(c) =
(14+1)/5


f'(c) = 15/5


f'(c) =
3 (1)


But f'(c) = 2c + 2
(2).


We'll substitute (1) in
(2):


2c + 2 = 3


2c =
3-2


2c = 1


c =
1/2


For x = 1/2, the mean
value theorem is satisfied for the function f(x) =
x^2+2x-1.

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