find the partial derivative of
$$f(x,y) = \ln(x+\sqrt{(x^{2}+y^{2})}); f_x(3,4)$$
so I found the partial derivative to be:

$$f_x(x,y) = (\frac{1}{x + \sqrt{x^2 + y^2}})(\frac{2x+1}{2\sqrt{x^2+y^2}})$$

how do I answer this question?

Question

find the partial derivative of 
$$f(x,y) = \ln(x+\sqrt{(x^{2}+y^{2})});  f_x(3,4)$$
so I found the partial derivative to be:

$$f_x(x,y) = (\frac{1}{x + \sqrt{x^2 + y^2}})(\frac{2x+1}{2\sqrt{x^2+y^2}})$$

how do I answer this question?

anonymous · Answer

You are sooo close!  The question looks like it is asking for a specific point.  You solved for the partial derivative in general.  Just plug in the point!

anonymous · Answer

Hold on... I think you need to check your chain rule again...

anonymous · Answer

yeah I think I computed the derivative incorrectly

anonymous · Answer

It simplifies a lot!  Just plug it in after you get the derivative.

anonymous · Answer

I'm far to lazy to simplify, yeah I got it

(1/(3+(3^(2) + 4^(2))^(1/2))(1+(2(3))/(2(3^(2)+4^2)^(1/2))))

anonymous · Answer

ok thanks for clarifying :)

anonymous · Answer

That should simplify to $$ \frac{1}{\sqrt{x^2 + y^2}}$$

anonymous · Answer

But I don't know... I got lost in the parentheses.