Need hint on 'simple' differentiation problem

[redshift]

I need to differentiate z = artan(y/x) with respect to x. Somehow z' = y/(1 +(1/x)^2) doesn't seem right.

[Nylex]

The derivative of arctan x = 1/(1 + x^2). There's a proof of that here (http://www-math.mit.edu/~djk/18_01/chapter20/proof02.html).

[dextercioby]

I need to differentiate z = artan(y/x) with respect to x. Somehow z' = y/(1 +(1/x)^2) doesn't seem right.

You know that
[\arctan(f(x))]'=\frac{f'(x)}{1+f^2 (x)}
,so apply the formula correctly.This is of course if "y" and "x" are independent variables.

[HallsofIvy]

z'= \frac{1}{1+(\frac{y}{x})^2} \(-\frac{y}{x^2}\)
by the chain rule.

Now multiply both numerator and denominator by x2.

[dextercioby]

z'= \frac{1}{1+(\frac{y}{x})^2} \(-\frac{y}{x^2}\)
by the chain rule.

Now multiply both numerator and denominator by x2.

Apparently the sofware didn't read the paranthesis you've written,so it should be:
z'= \frac{1}{1+(\frac{y}{x})^2} (-\frac{y}{x^2}) =-\frac{y}{x^2+y^2}