# Partial derivative question.

1. Feb 26, 2012

### Teachme

1. The problem statement, all variables and given/known data
I can't seem to find information on this specific question i have.

So i'm taking the partial derivative of this equation for both x and y
I know how to do it for y, but I am not seeing something with respect to x
fx(x,y)= x^7 + 2^y + x^y

2. Relevant equations

3. The attempt at a solution

So this is what I thought it should be

7x^6 + 1 + yx^(y-1)

I guess the answer is 7x^6+yx^(y-1) according to cramster and there is no 1 in it.

Why does 2^y not go to 1?

I would think because you treat y as a constant that it would go to zero and 2^0 is 1
What is wrong with my reasoning?

2. Feb 26, 2012

### SammyS

Staff Emeritus
If you treat y as a constant, then 2y is also a constant.

3. Feb 27, 2012

### Bacle2

Have you considered using the identity:

a^b =e^{bloga} ?

4. Feb 27, 2012

### HallsofIvy

First, stop even thinking Z"it goes to"! That is too vague and you are confusing yourself. The derivative of a constant is 0 but that does NOT mean that y itself is 0.