Derivative of cosx/lnx

The solution

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cos(x)
------
log(x)

$$\frac{\cos{\left(x \right)}}{\log{\left(x \right)}}$$

cos(x)/log(x)

Detail solution

Apply the quotient rule, which is:

$\frac{d}{d x} \frac{f{\left(x \right)}}{g{\left(x \right)}} = \frac{- f{\left(x \right)} \frac{d}{d x} g{\left(x \right)} + g{\left(x \right)} \frac{d}{d x} f{\left(x \right)}}{g^{2}{\left(x \right)}}$

$f{\left(x \right)} = \cos{\left(x \right)}$ and $g{\left(x \right)} = \log{\left(x \right)}$ .

To find $\frac{d}{d x} f{\left(x \right)}$ :
1. The derivative of cosine is negative sine:
  
  $\frac{d}{d x} \cos{\left(x \right)} = - \sin{\left(x \right)}$
To find $\frac{d}{d x} g{\left(x \right)}$ :
1. The derivative of $\log{\left(x \right)}$ is $\frac{1}{x}$ .
Now plug in to the quotient rule:

$\frac{- \log{\left(x \right)} \sin{\left(x \right)} - \frac{\cos{\left(x \right)}}{x}}{\log{\left(x \right)}^{2}}$
Now simplify:

$- \frac{\sin{\left(x \right)}}{\log{\left(x \right)}} - \frac{\cos{\left(x \right)}}{x \log{\left(x \right)}^{2}}$

The answer is:

$- \frac{\sin{\left(x \right)}}{\log{\left(x \right)}} - \frac{\cos{\left(x \right)}}{x \log{\left(x \right)}^{2}}$

The graph

Plot the graph f(x)

Plot the graph f'(x)

The first derivative [src]

  sin(x)     cos(x) 
- ------ - ---------
  log(x)        2   
           x*log (x)

$$- \frac{\sin{\left(x \right)}}{\log{\left(x \right)}} - \frac{\cos{\left(x \right)}}{x \log{\left(x \right)}^{2}}$$

Simplify

The second derivative [src]

                     /      2   \       
                     |1 + ------|*cos(x)
          2*sin(x)   \    log(x)/       
-cos(x) + -------- + -------------------
          x*log(x)         2            
                          x *log(x)     
----------------------------------------
                 log(x)

$$\frac{- \cos{\left(x \right)} + \frac{2 \sin{\left(x \right)}}{x \log{\left(x \right)}} + \frac{\left(1 + \frac{2}{\log{\left(x \right)}}\right) \cos{\left(x \right)}}{x^{2} \log{\left(x \right)}}}{\log{\left(x \right)}}$$

Simplify

The third derivative [src]

                                     /      3         3   \                
             /      2   \          2*|1 + ------ + -------|*cos(x)         
           3*|1 + ------|*sin(x)     |    log(x)      2   |                
3*cos(x)     \    log(x)/            \             log (x)/                
-------- - --------------------- - ------------------------------- + sin(x)
x*log(x)          2                            3                           
                 x *log(x)                    x *log(x)                    
---------------------------------------------------------------------------
                                   log(x)

$$\frac{\sin{\left(x \right)} + \frac{3 \cos{\left(x \right)}}{x \log{\left(x \right)}} - \frac{3 \left(1 + \frac{2}{\log{\left(x \right)}}\right) \sin{\left(x \right)}}{x^{2} \log{\left(x \right)}} - \frac{2 \left(1 + \frac{3}{\log{\left(x \right)}} + \frac{3}{\log{\left(x \right)}^{2}}\right) \cos{\left(x \right)}}{x^{3} \log{\left(x \right)}}}{\log{\left(x \right)}}$$

Simplify

The graph

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Derivative of cosx/lnx

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The solution