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    f(t) = K(t) - K(t-T)

    I want to find  \frac{df}{dt}

    i'm unsure of the notation, does the 3rd term represent K as a function of t-T :facepalm:? I know the 2nd term is showing K is a function of time otherwise it would be written simply Kt, but unsure of the 3rd term. I'm confused
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    Oh btw I believe the answer to be

     \frac{df}{dt} = \frac{dK}{dt} - K(t) - t\frac{dK}{dt} + T\frac{dK}{dt}

    because K can't be a function of t then t-T in the same equation, so it must mean f(t) = K(t) - tK(t) + TK(t)
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    It does indeed mean K is a function of T-t, where I am assuming T is a constant?
    You could differentiate it by using the substitution u=T-t and then the chain rule, should work through fairly easily.
 
 
 
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