Originally Posted by

**GreenMachine** So, I've been studying all day, but am really thrown off by these three practice problems. One is:

1.) True/False: If f is a function of one variable and u=f(x-y), then uxx=uyy. (those x and y's are subscripts)

My question is why would a function of one variable even have partial derivatives.

2.) True/False: if w=(sin(y))e^x, x=s-t, y=st, then wxt (the x and t are subscript) at s=1, t=1, is 3.

Is this some form of chain rule? I don't understand how the x=s-t changes this.

3.) Use the linear approximation or differentials to find an approximation to [26.98]^1/3 times [36.04]1/2

There are absolutely NO problems in the book like this, and we never discussed it, so I have NO idea how to approach this.

Please, anyone answer as many as you can. I'm really frustrated and have no idea how to approach these problems. Thank you.