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| Interpretation of Derivative at a Point |
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| Let P(x,y) and Q(x + Dx,y + Dy) be two neighbouring points on the curve y = f (x). |
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Let TPT' be the tangent at P, PQ is called the secant of the curve
and the slope of secant  . |
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| Let Q (t) be a quantity that changes with time 't'. |
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Let Dt be the increment given to 't' and DQ be the corresponding increment in Q, then 
is called the average rate of change of Q with respect to 't'. (Also known as Newton - quotient of f at t) |
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| Note: |
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| If 's' is the displacement of a particle at time 't' and let s = Q(t), |
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