Derivatives of Constant Multiples

Example:
f(z) = 7*ln(5*z-5)

The first thing to notice when finding the derivative of this function is that it is the product of a constant and another function, as shown in color below:

f(z) = 7 ln(5*z-5)

The Derivative Rule for Constant Multiples:

The derivative of a constant multiple is the constant times thederivative of the function.
If
  z = c ( f(x) )
then the derivative of z is
  z' = ( c f(x) )'
    = c f '(x)

So our example,

f(z) = 7 ln(5*z-5)
we can think of as
f(z) = c g(z)
So the derivative is
f '(z) = ( c g(z) )'
  = c g '(z)  
  = 7 (ln(5*z-5))'  
and we just need to know the derivative on the right-hand side of the equation. In this case this is
ln(5*z-5) = 5*(5*z-5)-1 (-5)*z-6 (by the chain rule)
so the finished derivative is
f '(z) = 7 ( 5*(5*z-5)-1 (-5)*z-6 )
  = (-175)*z-6 (5*z-5)-1
[]


additional explanation for the derivative of constant multiples
see another derivative of constant multiples example
practice gateway test
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Comments to Gavin LaRose
glarose@umich.edu
©2001 Gavin LaRose, University of Michigan Math Dept.