By the Mean Value Theorem, there exists some \( c \) in the interval \( (a, b) \) such that
\[ f'(c) = \frac{f(b) - f(a)}{b-a} = \frac{b^{n+1} - a^{n+1}}{b-a}. \]
The derivative \( f'(x) = (n+1)x^n \). Therefore,
\[ \frac{b^{n+1} - a^{n+1}}{b-a} = (n+1)c^n.
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