1. anonymous

@phi

2. anonymous

3. anonymous

@dan815

4. anonymous

@robtony

5. jim_thompson5910

were you able to find dy/dx ?

6. anonymous

yes, I have the prime derivative I got -3x/y

7. jim_thompson5910

correct $\Large \frac{dy}{dx} = \frac{-3x}{y}$

8. jim_thompson5910

Now apply the derivative to both sides $\Large \frac{dy}{dx} = \frac{-3x}{y}$ $\Large \frac{d}{dx}\left[\frac{dy}{dx}\right] = \frac{d}{dx}\left[\frac{-3x}{y}\right]$ $\Large \frac{d^2y}{dx^2} = ??$

9. anonymous

and then for the y'' i got -3y-y'(-3x) --------- 4y^2

10. anonymous

and then I plug -3x/y on the y' right?

11. jim_thompson5910

correct and simplify

12. anonymous

-3y+(9x/y) ---------- 4y^2

13. jim_thompson5910

I'm not getting the same thing

14. anonymous

@jim_thompson5910 , from this pint do I just plug the values of x and Y?

15. anonymous

what did you get?

16. anonymous

|dw:1438995573413:dw|

17. jim_thompson5910

$\Large \frac{d^2y}{dx^2} = \frac{-3y-(-3x)\frac{dy}{dx}}{y^2}$ $\Large \frac{d^2y}{dx^2} = \frac{-3y+3x\left(\frac{-3x}{y}\right)}{y^2}$ $\Large \frac{d^2y}{dx^2} = \frac{-3y-\frac{9x^2}{y}}{y^2}$ $\Large \frac{d^2y}{dx^2} = \frac{-3y{\color{red}{*y}}-\frac{9x^2}{y}{\color{red}{*y}}}{y^2{\color{red}{*y}}}$ $\Large \frac{d^2y}{dx^2} = \frac{-3y{\color{red}{*y}}-\frac{9x^2}{\cancel{y}}{\color{red}{*\cancel{y}}}}{y^2{\color{red}{*y}}}$ $\Large \frac{d^2y}{dx^2} = \frac{-3y^2-9x^2}{y^3}$

18. anonymous

oh I see you simplified it, and from here. Do I plug the x and y values into this derivate?

19. jim_thompson5910

yeah

20. anonymous

-2.625?

21. jim_thompson5910

yeah, -21/8 = -2.625

22. anonymous

okay, if they say that I need to put my answer into 2 decimal places, do i put -2.63?

23. jim_thompson5910

yes

24. anonymous

okay, thank you so much

25. jim_thompson5910

no problem