Thread: help with find values

I have a simple yet frustrating problem.

V=15

h= 2.54

r= ?

V= pi*h(3r^2 + h^2) / 6

what is the value of r?

Now I need a complete break down of the reasons for the working of this equation.

I have asked sevral sites and the explanations are difficult to understand.

I need it in plain english.

Someone said I had to divide V/(3*pi*h) to find r

now what i want to know is what formula he used to come to that decision telling me the answer like that is no good.

what i need is to know why make descisionlike this so i can solve ALL algrebra question.

please help

I am looking for somone who will also perhaps be will to PM so i can understand

thank you

You are given a formula with variables V, h, and r.

You are given values for V and h.

You are asked for the corresponding value of r.

Plug the number for V in for V in the formula..

Plug the number for h in for h in the formula.

Simplify as much as you can.

Solve the resulting quadratic equation for the value of r.

If you get stuck or do not understand a step, please reply showing your progress and clearly stating where you are getting confused. Thank you!

Originally Posted by Mathaticaln00b

I have a simple yet frustrating problem.

V=15

h= 2.54

r= ?

V= pi*h(3r^2 + h^2) / 6

what is the value of r?

Now I need a complete break down of the reasons for the working of this equation.

I have asked sevral sites and the explanations are difficult to understand.

I need it in plain english.

Someone said I had to divide V/(3*pi*h) to find r

now what i want to know is what formula he used to come to that decision telling me the answer like that is no good.

what i need is to know why make descisionlike this so i can solve ALL algrebra question.

please help

I am looking for somone who will also perhaps be will to PM so i can understand

thank you

Hi Mathaticaln00b,



Substitute what you know...V=15, h=2.54...




Apply the distributive property...



Clear the fraction (Multiply both sides by 6)...



Subtract 16.387064 from both sides...



Divide both sides by ...



Take the square root of both sides...

Originally Posted by masters

Hi Mathaticaln00b,



Substitute what you know...V=15, h=2.54...




Apply the distributive property...



Clear the fraction (Multiply both sides by 6)...



Subtract 16.387064 from both sides...



Divide both sides by ...



Take the square root of both sides...

hi thanks to both of you for answering my post.

I have a few questions though since i still dont know what r value is.

please tell me if i am supposed to know or not.

I figured out to a point that substition of values makes sense but to be honest i dont understand the rest of it.

also when using pi in the equation am i using the number 3.14 or not?

theres so much i dont understand please help me.

what i did was

v=3.14 x 2.54(3 x 3.14 x 2.54 x 2) + (3.14 x 2.54 x 2.54 x 2.54) / 6

then i x that by 3 and squared it

then i did 2.54 squared

and then divided by 6

i know this is wrong but im so confused

You said you were solving for r. You have a "v" in your final equation but no "r". what happened to it?

You wrote "v=3.14 x 2.54(3 x 3.14 x 2.54 x 2) + (3.14 x 2.54 x 2.54 x 2.54) / 6"

Okay, that first "3.14 x 2.54" is pi h but then the first thing inside your parentheses should be "3r^2". Instead you appear to have pi h times 2. Why? The second term inside the parenthes should be h^2 instead you have a separate parentheses and pi h^3. That, at least is correct: pi h (h^2)= pi h^3. Even assuming that the "x 2" should be "^2", your first term is pi h(3 pi h^2) instead of 3r^2. Are you just putting numbers together at random? Why not do what was suggested in the first response?