Got Homework?
Connect with other students for help. It's a free community.
Here's the question you clicked on:
 0 viewing

This Question is Closed

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
\[\large 0=\frac{ r2700 }{ r^2 }+62 \pi r\]
 one year ago

calculusxy Group TitleBest ResponseYou've already chosen the best response.0
You are trying to find the area of a radius?
 one year ago

calculusxy Group TitleBest ResponseYou've already chosen the best response.0
Sorry I meant the area of a circle.
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
No it's an optimization problem I am trying to do, I just need to solve for 'r'
 one year ago

calculusxy Group TitleBest ResponseYou've already chosen the best response.0
Oh I thought that because the formula to finding the area of a circle,you have to first square the radius and then multiply it by pi (r^2)3.14.
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Multiply everything by r^2. Then factor out an r. From there it's a quadratic.
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Oh my bad. You actually get a cubic.
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
top and bottom or just top?
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Multiply everything by r^2. When you multiply the fraction, multiply on top.
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
\[r^2 or \frac{ r^2 }{ r^2 }\]
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Just r^2
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
yeah so woulnt that cancel out with the fraction
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Yes =) That's the point. It gets r out of the denominator.
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
ohh i thought you were also telling me to muktiply the top by r^3 so the function would be diff, i misunderstood
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
\(\huge 0 = \frac{r2700}{r^2} + 62\pi*r\) multiply everything by r^2 \(\huge (0)*r^2 = (\frac{r2700}{r^2})*r^2 + (62\pi*r)*r^2\)
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Gives: \(\huge 0 = r2700 + 62\pi*r^3\)
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
And honestly from there your best bet is to use a cubic solver of some sort. Wolfram Alpha should do just fine.
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
dw:1371520632051:dw yeah but the thing is like during an exam i cant use it :P
 one year ago

Bad2zBone Group TitleBest ResponseYou've already chosen the best response.0
Are you sure the question is correct?
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
@Bad2zBone yes
 one year ago

Bad2zBone Group TitleBest ResponseYou've already chosen the best response.0
I suggest you double check, because you will not solve this without the aid of wolfaplha
 one year ago

burhan101 Group TitleBest ResponseYou've already chosen the best response.0
here is the question and my solution
 one year ago

Bad2zBone Group TitleBest ResponseYou've already chosen the best response.0
I suggest you take a look at this http://gbbservices.com/math/cubic.html
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Okay on the step where you take C', you make incorrect use of the quotient rule. The derivative of the top will be 0.
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
The correct derivative is: \(\Large C' = \frac{27900}{r^2} + 62\pi*r\)
 one year ago

SmoothMath Group TitleBest ResponseYou've already chosen the best response.1
Set the derivative equal to 0 and solve: \(\Large \frac{27900}{r^2} + 62\pi*r = 0\) \(\Large (\frac{27900}{r^2} + 62\pi*r)*r^2 = 0*r^2\) \(\Large 27900 + 62\pi*r^3 = 0\) \(\Large 62\pi*r^3 = 27900\) You good from there?
 one year ago
See more questions >>>
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.