Hi,

I need help to derivate the following equation :

Arc tan (square(x-1)/x)

I can't get the correct answer which is : (2-x)/2(x^2+x-1) square (x-1)

Here is what I've done so far :

du/a^2+u^2

so :

du = 1/2square(x-1)

a^2 = x^2

u^2 = (x-1)

which give me :

1/2(x^2+x-1) square (x-1)

can't find where the 2 - x come from

thx for the help