Thursday, May 20, 2010

`y = xarctan(2x)-1/4ln(1+4x^2)` Find the derivative of the function

The derivative of y in terms of x is denoted by  `(dy)/(dx)` or `y’'`


 For the given problem: `y = xarctan(2x) -1/4ln(1+4x^2)` , we may apply the basic differentiation property:


`d/(dx) (u-v) = d/(dx) (u) - d/(dx) (v)`


Then the derivative of the function can be set-up as:


`d/(dx)y =d/(dx)[ xarctan(2x) -1/4ln(1+4x^2)]`


`y ' = d/(dx) xarctan(2x) -d/(dx) 1/4ln(1+4x^2)`



For the derivative of `d/(dx)[ xarctan(2x)` , we apply the Product Rule: `d/(dx)(u*v) = u’*v =+u*v’` .


`d/(dx)[ xarctan(2x)] = d/(dx)(x) *arctan(2x)+ x * d/(dx)arctan(2x)` .


Let `u=x` then ` u' = 1`


   `v=arctan(2x)` then `dv= 2/(4x^2+1)`


Note: `d/(dx)arctan(u)= (du)/(u^2+1)`



Then,


`d/(dx)(x) *arctan(2x)+ x * d/(dx)arctan(2x)`


`= 1 * arctan(2x) +x * 2/(4x^2+1)`


`= arctan(2x) +(2x)/(4x^2+1)`



For the derivative of  `d/(dx) 1/4ln(1+4x^2)` , we apply the basic derivative property:


`d/(dx) c*f(x) = c d/(dx) f(x)` .


Then,


`d/(dx) 1/4ln(1+4x^2)= 1/4 d/(dx) ln(1+4x^2)`


Apply the basic derivative formula for natural logarithm function: `d/(dx) ln(u)= (du)/u` .


 Let `u =1+4x^2` then `du = 8x`


`1/4d/(dx) ln(1+4x^2) = 1/4 *8x/(1+4x^2)`


                             ` =(2x)/(1+4x^2)`



Combining the results, we get:


`y' = d/(dx)[ xarctan(2x)] -d/(dx)[ 1/4ln(1+4x^2)]`


`y ' = [arctan(2x) +(2x)/(4x^2+1)] - (2x)/(1+4x^2)`


`y ' = arctan(2x) +(2x)/(4x^2+1) - (2x)/(1+4x^2)`


`y ' = arctan(2x) +0`


`y'=arctan(2x)`

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