how would you differentiate this equation??

dy/dx + e^(x+y) = 0

Are you sure you want it differentiated? it looks more like a differential equation that one might want to solve. This can be done by rewriting it as

dy/dx = -e^x * e^y
dy/e^y = -dx*e^x
e^-y dy = -e^x dx
Integrate both sides
-e^-y = -e^x + C where c is an abrbitrary constant
This can be rewritten as y(x)