Calculus 1 Lecture Notes, Section 2.9

Proof: Case #1: f(x) is constant on [a, b]. Then f ( (c) = 0, because the derivative of a constant is zero. Case #2: f(x) is not constant on [a, b]. It must be the case then that f(x) increases to the right of a, or that f(x) decreases to the right of a. ... where is the equation of the secant … ................
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