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Verify MVT hypotheses and find the guaranteed value of c

Consider the function f(x)=exf(x) = e^x on the closed interval [0,2][0,2].

The function f(x)=exf(x) = e^x is continuous on [0,2][0,2] and differentiable on (0,2)(0,2), so the Mean Value Theorem guarantees the existence of at least one number cc in (0,2)(0,2) such that

f′(c)=f(2)−f(0)2−0.f'(c) = \frac{f(2) - f(0)}{2 - 0}.

Find the exact value of cc guaranteed by the Mean Value Theorem for f(x)=exf(x) = e^x on [0,2][0,2].

Hint

Compute the average rate of change f(2)−f(0)2−0\frac{f(2)-f(0)}{2-0}, then set f′(c)f'(c) equal to that value and solve for cc using logarithms.

Step-by-step solution

First compute the slope of the secant line: f(2)−f(0)2−0=e2−e02=e2−12\frac{f(2)-f(0)}{2-0} = \frac{e^2 - e^0}{2} = \frac{e^2 - 1}{2}. Since f(x)=exf(x)=e^x is continuous everywhere and differentiable everywhere, both hypotheses of the MVT are satisfied on [0,2][0,2], so a valid cc in (0,2)(0,2) must exist.

Since f′(x)=exf'(x) = e^x, we need ec=e2−12e^c = \frac{e^2-1}{2}. Taking the natural logarithm of both sides gives c=ln⁡(e2−12)c = \ln\left(\frac{e^2-1}{2}\right). Numerically this is approximately c≈1.13c \approx 1.13, which indeed lies in (0,2)(0,2) as required.

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