Tuesday, June 23, 2015

`h(t) = log_5(4-t)^2` Find the derivative of the function

Derivative of a function h with respect to t is denoted as h'(t).


 The given function: `h(t) = log_5(4-t)^2` is in a form of a logarithmic function.


From the derivative for logarithmic functions, we follow:



`d/(dx)log_a(u) =((du)/(dx))/(u*ln(a)) `



By comparison: `log_5(4-t)^2` vs.`log_a(u)` we should let:


`a=5 ` and `u = (4-t)^2`


 For the derivative of u, recall the Chain Rule formula:


`d/(dx)(f(g(x)))= f'(g(x))*g'(x)`


Using `u=(4-t)^2` , we let:


`f(t) = t^2`


`g(t) = 4-t` as the inner function


`f'(t)= 2t`


`f'(g(t))= 2*(4-t)`


`g'(t)= (-1)`


Following the Chain Rule formula, we get:


`d/(dx) (4-t)^2= 2 *(4-t)*(-1)`


`d/(dx) (4-t)^2= -2*(4-t)`


or


`(du)/(dx)=-2*(4-t)`


 Plug-in the values:


`u =(4-t)^2` ,     `a=5 `  ,  and `(du)/(dx)=-2*(4-t)`


 in the `d/(dx)log_a(u) =((du)/(dx))/(u*ln(a))` , we get:


`d/(dx) (log_5(4-t)^2) = ((-2)*(4-t))/((4-t)^2ln(5))`


Cancel out common factor (4-t):


`d/(dx) (log_5(4-t)^2) = -2/((4-t)ln(5))`


 or` h'(t)= -2/((4-t)ln(5))`

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