Partial diffrentiation HELP

[theaviator]

Partial diffrentiation...URGENT PLZ HELP

Here are the two problems...

1- If U=(X,Y) X=F(R,S) Y=G(R,S)

SHOW THAT: Urr=(Wxx) (Fr)^2 + 2(Wxy) (Fr) (Gr)^2 + (Wx) (Frr) + (Wy)+ (Grr)


2- SHOW THAT: U(R,K)=R^n Cos(nk) satisfies the equation
Urr+1/r U + 1/(r^2) Ukk=0


that's urgent please help now if u can...thanks

 

[cristo]

You need to show some work before we can help you. Also, what is W in the first question? You have not defined it! For the second one, you simply take the required derivatives of U and plug then in.

 

[HallsofIvy]

Use the chain rule- twice.