Monday 3 August 2015

`y = 1/2 (1/2ln((x+1)/(x-1)) + arctanx)` 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 = 1/2(1/2ln((x+1)/(x-1)) +arctan(x))` , we may apply the basic differentiation property: `d/(dx) c*f(x) = c d/(dx) f(x)` .


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


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


Apply the basic differentiation property: `d/(dx) (u+v) = d/(dx) (u) + d/(dx) (v)`


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


For the derivative of `d/(dx)(1/2ln((x+1)/(x-1)))` , we may apply again the basic derivative property:`d/(dx) c*f(x)...

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


 For the given problem: `y = 1/2(1/2ln((x+1)/(x-1)) +arctan(x))` , we may apply the basic differentiation property: `d/(dx) c*f(x) = c d/(dx) f(x)` .


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


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


Apply the basic differentiation property: `d/(dx) (u+v) = d/(dx) (u) + d/(dx) (v)`


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


For the derivative of `d/(dx)(1/2ln((x+1)/(x-1)))` , we may apply again the basic derivative property:`d/(dx) c*f(x) = c d/(dx) f(x)` .


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


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


 Let `u =(x+1)/(x-1)` then `du = -2/(x-1)^2` .


 Note For the derivative of `u=(x+1)/(x-1)` ,we apply the Quotient Rule: `d/(dx)(f/g) = (f'*g-f*g')/g^2` .


Let:


`f= (x+1)` then `f'=1`


`g=(x-1)` then `g'=1`


Then,


`d/(dx)((x+1)/(x-1))= (1*(x-1)-(x+1)*(1))/(x-1)^2`


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


                 ` =(x-1-x-1)/(x-1)^2`


                ` =(-2)/(x-1)^2`


Applying: `d/(dx) ln(u)= (du)/u` on:


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


                                     `=(1/2) *((-2)/(x-1)^2)*(x-1)/(x+1)`


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


Cancel common factors 2 and `(x-1)` from top and bottom:


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


Recall `(x-1)*(x+1) = x^2-x+x-1 = x^2-1` then the derivative becomes:


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



For the derivative of `d/(dx)(arctan(x))` , we apply basic derivative formula for inverse tangent:


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



Combining the results, we get:


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


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


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


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


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


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


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


or


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

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