Hello,

Can someone please explain how implicitly differentiating u(x_{1},x_{2}(x_{1})) = k with respect to x_{1}yields du(x_{1},x_{2})/dx_{1}+ du(x_{1},x_{2})/dx_{2}* dx_{2}/dx_{1}= 0 ?

The textbook I'm reading just makes the statement and I'm not sure how it works out that way.

Thanks!