As Maths Differentiation

What have you done so far?

not quite sure how to do the next step though :/

Im not sure what i'm doing from here on aha I've totally lost what i should be doing :/

ah okay I'll try that but this whole thing has confused me haha what answer do you end up with? I keep messing up somewhere

So once you have your differentiated equation, you need to use it to find a stationary point (which you can then determine as a point of inflection, maximum or minimum).

Do you know how to find a stationary point?

I don't think im differentiating correctly. I missed a few lessons on it :/



does this become 2piR + ??? i dont know how to differentiate this section

I thought it was that but i wasn't sure. Okay so i had that but this is where i think i am going wrong. What should i be doing after this step?

What have you got now then?

I have 2piR+1000r^-1

Not quite - $1000r^{-1}$ is just a rewrite of $\frac {1000}{r}$, you need to then differentiate it.

Ah yes i just did that i ended up with the answer 2.06 :/ if i didnt make a mistake i believe this is correct but i got -1000r^-2 i think aha

The differentiation is correct, but the answer is not what I have.

You should have then ended up with $\frac{dA}{dr}=2 \pi r - 1000r^{-2}$ (or $\frac{dA}{dr}=2 \pi r - \frac {1000}{r^2})$

To find a stationary point you need $\frac{dA}{dr}=0$. The stationary point can then be determined to be a minimum.

If you have done all that, then I'll need to see what you did to get to the answer.

so i can rewrite this as equal 0. is that correct? and then i can just rearrange by moving thing to other sides?