Implicit differentiation dy/dx

[freetofu]

Homework Statement

Determine dy/dx
xy^-2 = 1

Homework Equations

The Attempt at a Solution

Here's what I tried:
y^-2 - 2xy^-3(dy/dx) = 1
dy/dx = (y - y^3)/2x

The answer in the book is y/2x. How do you do it?

 

[rock.freak667]

You differentiated the left side but not the right side

d/dx(1) = ?

 

[freetofu]

Thanks. Duh.