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- A function f(x) defined on an open interval (a,b) is said to be differentiable or derivable in open interval (a,b) if it is differentiable at each point of (a,b)
- A function f(x) defined on [a,b] is said to be differentiable or derivable at the end points a and b if it is differentiable from the right at a and from the left at b.
In other words
“If f is derivable in the open interval (a,b) and also at the end points a and b, then f is said to be derivable in the closed interval[a,b]”.
“A function f is said to be a differentiable function if it is differentiable at every point of its domain” -