Partial derivatives and power rule

[bobsmith76]

Homework Statement

∂f/∂x (xy -1)² = 2y(xy-1)

The Attempt at a Solution

I would think the answer would be

2(xy-1)

I don't understand where the y comes from in 2y

 

[Dick]

Homework Statement

∂f/∂x (xy -1)² = 2y(xy-1)

The Attempt at a Solution

I would think the answer would be

2(xy-1)

I don't understand where the y comes from in 2y

It comes from the chain rule. Look it up!

 

[bobsmith76]

It looks like they're using u substitution

(u)² = 2u

u = xy - 1
du or ∂f/∂x(not sure about the notation) = y

2u * y = 2y(u), insert u = 2y(xy-1)

 

[bobsmith76]

i solved the problem before I saw dick's reply