Answer 1

`e^x + e^y = e^(x – y)`  

diff. w.r.t. x 

`(de^x)/dx+(de^y)/dx=(de(x-y))/dx` 

`e^x + e^y dy/dx=e^(x-y) (1-dy/dx)` 

`(e^y + e^(x – y))dy/dx=e^(x-y)-e^x` 

`dy/dx=((e^(x-y)-e^x)/(e^(x-y+e^y)))=(e^x+e^y-e^x)/(e^x+e^y+e^y)`