Originally Posted by

**econolondon** Hi

I am trying to get the total differential for

y = x_{1}x_{2}/2x_{1} + x_{2}

I have been given the answer

dy = [x_{2}/2x_{1} + x_{2}]dx_{1} - [2x_{1}x_{2}/(2x_{1}+x_{2})^2]dx_{1} + [x_{1}/2x_{1} + x_{2}]dx_{2 }- [x_{1}x_{2}/(2x_{1}+x_{2})^2]dx_{2 }

Is this right?

It is my understanding that the general formula is F_{1}dx_{1} + F_{2}dx_{2}, for y=F(x_{1},x_{2})

I don't understand why, in the second and fourth terms of the answer, the WHOLE of the denominator is being squared, rather than just the x_{1 }or x_{2} that the partial derivative refers to......