Show that `f(x)=tan^(-1)x-x` is decreasing function on `Rdot`

Explanation

`f(x)=tan ^-1 x-x`

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

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

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

We know,

`x^2 geq 0,1+x^2>0, forall x in R `

`therefore -x^21+x^2<0, forall x in R `

`Rightarrow f^prime(x)<0, forall x in R`

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