Thursday, November 4, 2010

`f(x) = arctan(sqrt(x))` Find the derivative of the function

The given function `f(x) = arctan(sqrt(x))` is in a inverse trigonometric form.


The basic derivative formula for inverse tangent is:


`d/(dx) arctan(u) = ((du)/(dx))/sqrt(1-u^2)` .


 Using u-substitution, let `u = sqrt(x)` then
`u^ 2 = (sqrt(x))^2 = x`


For the derivative of u or `(du)/(dx)` , we apply the Power Rule:


`d/dx(x^n)=n*x^(n-1) * d(x)`


This is possible since `sqrt(x) = x^(1/2)`


Then    ` d/(dx) x^(1/2) = 1/2 * x^(1/2-1)* 1`            Note: `d/(dx) (x) = 1`


                     `=1/2 x^(-1/2) `


Applying the Law of Exponents: `x^(-n)=1/x^n` .


`(du)/(dx) =1/2 * x^(-1/2) `   


      `= 1/2 * 1/ x^(1/2)`


       ` =1/(2 x^(1/2) ) or1/(2 sqrt(x))`



We now have: `u=sqrt(x)` and `(du)/(dx) =1/(2sqrt(x))` .


 Applying the formula` d/(dx) arctan(u)= ((du)/(dx))/(1+u^2)` :


`f'(x) = d/(dx)arctan(sqrt(x))=(1/(2sqrt(x)))/(1+(sqrt(x))^2)`


`f'(x) =(1/(2sqrt(x)))/(1+x)`


`f'(x) =1/(2sqrt(x))* 1/(1+x) `        


`f'(x) =1/(2sqrt(x)(1+x))`

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