# Some partial derivatives

• July 28th 2009, 12:46 AM
drew.walker
Some partial derivatives
I've been asked to find the partial derivative with respect to x for the function:

$
f(x,y) = 2xe^{x+y^2} - e^y + sinh(2x + y)
$

I've learnt about treating y as though it's a constant, and this is what I've got so far. However, I think my working is wrong or my rules haven't been applied correctly. My logic was to apply the product rule to the first grouping, treat e^y just as a constant and just differentiate the last grouping based on the rules for sinh. Here's the result I got:

$
f_x(x,y) = 2x({e^{x+y^2}}\cdot{1}) + {e^{x+y^2}}\cdot{2} - 0 + {cosh(2x + y)}\cdot{2}
$

$
f_x(x,y) = 2e^{x+y^2}(x + 1) + 2cosh(2x+y)
$

Hopefully someone can shed some light on whether the working/answer is correct? I'm not feeling very confident about it.
• July 28th 2009, 01:44 AM
songoku
I think you got it right
• July 28th 2009, 05:12 AM
drew.walker
Same problem with respect to y
What about if I was to take the partial derivative with respect to y? Would it be:

$
f_y(x,y) = 2x({e^{x+y^2}}\cdot{2y}) + {{e^{x + y^2}}\cdot{0}} - e^y + {cosh(2x + y)} \cdot {1}
$

$
f_y(x,y) = 4xye^{x+y^2} - e^y + cosh(2x + y)
$
• July 28th 2009, 05:55 AM
songoku
Looks right