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| Derivative at a Point |
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| Let f be a function and a be any point in its domain. Let h>0 be a small number. |
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f(x) is said to be differentiable if 
exists and is denoted by f|(a), then f|(a) is called the derivative or differential coefficient of f(x) at x = a. That is |
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 as
x approaches a through values less than 'a' is called Left hand derivative at x=a denoted by Lf '(a). |
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as
x approaches a through values greater than 'a' is called Right hand derivative at x = a, denoted by Rf '(a). |
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| Let y = f (x). |
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| The derivative of f at x is denoted by f '(x). |
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| Finding the derivative of a function using the above definition is called differentiation from first principles. |
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