## artix_17 2 years ago Partial derivative, pls help !! f(w,z)= w(w^2+z^2)^-1 Find f'w

1. klimenkov

What is the biggest problem for you?

2. artix_17

I can't seem to get the answer

3. klimenkov

Do you know how to calculate the ordinary derivative, not the partial?

4. artix_17

Yes, for this question I use product rule, but just can't get the answer

5. klimenkov

Write here what you've got.

6. klimenkov

You can draw it using the "Draw" button.

7. artix_17

f'w = w X (-1)(w^2+z^2)^-2 X 2w + (w^2+z^2)^-1 (1) = -2w^3 (w^2+z^2) + (w^2+z^2)^-1

8. artix_17

= -2w^3 (w^2+z^2)^-2 + (w^2+z^2)^-1

9. klimenkov

You have to check the last answer very carefully. You are doing this right, but you are making mistakes. Check them.

10. artix_17

Which part is the mistake?

11. klimenkov

f'w = w X (-1)(w^2+z^2)^-2 X 2w + (w^2+z^2)^-1 - This is OK, but this = -2w^3 (w^2+z^2) + (w^2+z^2)^-1 is not. Try to find the common denominator in the first one and subtract the fractions.

12. artix_17

oh okay got it, thanks

13. klimenkov