## ashleynguyenx3 Group Title The sides of a square are increasing at a rate of 10 cm/sec. How fast is the area enclosed by the square increasing when the area is 150 cm^2. one year ago one year ago

1. asnaseer Group Title

start by assigning a variable to represent the side length of the square. lets call it x. now, what would be the area of the square in terms of x?

2. ashleynguyenx3 Group Title

100?

3. asnaseer Group Title

no - what is the area of a square if its side length is equal to x?

4. ashleynguyenx3 Group Title

I don't get it

5. asnaseer Group Title

|dw:1350248149705:dw|

6. ashleynguyenx3 Group Title

Oh, A=x^2

7. asnaseer Group Title

:)

8. asnaseer Group Title

good, so now you just need to differentiate both sides with respect to time (t). Do you know how to do that?

9. ashleynguyenx3 Group Title

Derivative, right?

10. asnaseer Group Title

yes

11. ashleynguyenx3 Group Title

dA/dt=2x(dx/dt)

12. asnaseer Group Title

perfect! almost there now...

13. asnaseer Group Title

now, when the area is 150 cm^2, then what would the side length of the square equal?

14. asnaseer Group Title

i.e. what is the length of the side of a square if its area is 150 cm^2?

15. ashleynguyenx3 Group Title

sq rt of 150?

16. asnaseer Group Title

yes

17. ashleynguyenx3 Group Title

So you would plug in x and dx/dt to get dA/dt?

18. asnaseer Group Title

now, in the equation you derived, you got:$\frac{dA}{dt}=2x\frac{dx}{dt}$Your questions tells you how fast the side length is increasing, so this gives you the value for:$\frac{dx}{dt}=10$

19. asnaseer Group Title

yes - you have it now - well done! :)

20. ashleynguyenx3 Group Title

Yay, thank you! :)

21. asnaseer Group Title

yw :)

22. ashleynguyenx3 Group Title

I would ask for more help, but it's okay.

23. asnaseer Group Title

?

24. ashleynguyenx3 Group Title

I don't really understand related rates.

25. asnaseer Group Title

What you should do is find a specific example and then post that as a question. Otherwise it becomes difficult to explain in general terms.

26. asnaseer Group Title

For example, in this question, the rate of increase of side length is RELATED to the rate of increase of area by the formula you just derived.

27. ashleynguyenx3 Group Title

Well, I'm just doing this packet. I understand some, but not all. http://tutorial.math.lamar.edu/ProblemsNS/CalcI/RelatedRates.aspx

28. asnaseer Group Title

In that case I would advise you to pick one that you don't understand and post it as a question. If you also include what parts of it you DO understand then it becomes easier for others to focus on the parts that you are having difficulties with.

29. ashleynguyenx3 Group Title

Okay, thanks again :D