C1 simultaneous equation? Difficult

A reply asap would be great considering I am revising and time is important! Thanks

That you have two answers might give you a clue that there's a quadratic involved.

So, since the second equation involves mostly r's, I'd find h as a function of r from the first equation, sub it into the second and solve for r.

so like h = 100-4r ?
because I tried that and ended up with:
200-6r=1400/r
I couldnt get past this, maybe I messed up, but I dunno. Could you possibly try it and see what you came up with?

Multiply through by r, and your quadratic appears.

sooo...
200r-6r^2=1400
the answers are in Pi so I have clearly gone wrong..

sooo...
200r-6r^2=1400
the answers are in Pi so I have clearly gone wrong..

RTQ

This quadratic gives you r

The question then asks for Volume

Rtq?

RTQ

This quadratic gives you r

The question then asks for Volume

how exactly do I get the value for r from this?
I have 100r-3r^2=700
that has 2 unknown factors. How can I work it out?

$3r^2 - 100r + 700 = 0$

Factorise
or
Complete the square

okay, thanks a bunch.
I got r=-10
&
r=70/3
does that sound right to you?

They should both be positive

(3r - 70)(r - 10) = 0

Thanks a bunch, appreciate the help & patience.

NP
http://tinypic.com/view.php?pic=25z6jut&s=8#.VIYp6zGsURk
next time - no maths after 10pm

One last question
Was wondering if you could help? :/
Got the first bit & second bit but for the third, not so much.
I did for the wood:
2y^2 + 7xy = 10000cm
&
6x^2 = 22500cm
so I divided by 6 then rooted and got 61.2 or something along those lines. I looked into the back of my book and they havent even written an answer in for me to check!?