Solve formula using transposition

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meano

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I need help with this please.

I think I am right in saying that to solve the following formula I need to use transposition but I am struggling with it. I have looked at similar formulas and still not able to do it with this one. The question is as follows:

The sag at the centre of a wire of length l supported at two points a distance d apart is given by the formula

s = sqrt 3d(l - d)/8

Find the length of wire to the nearest mm when d = 1.62m and s - 82cm.

I am ok with converting cm and m to mm but just struggling with the transposition.

Thanks
 
meano said:
I need help with this please.

I think I am right in saying that to solve the following formula I need to use transposition but I am struggling with it. I have looked at similar formulas and still not able to do it with this one. The question is as follows:

The sag at the centre of a wire of length l supported at two points a distance d apart is given by the formula

s = sqrt 3d(l - d)/8

Find the length of wire to the nearest mm when d = 1.62m and s - 82cm.

I am ok with converting cm and m to mm but just struggling with the transposition.

Thanks
Click to expand...

Why worry about transposition?

Simply substitute numbers for s (= 82) and d (=1.62) and solve for l.
 
Subhotosh Khan said:
Why worry about transposition?

Simply substitute numbers for s (= 82) and d (=1.62) and solve for l.
Click to expand...

Thanks for the reply. I understand this but as I don't have a value for l, what do I do with l in the formula to get the answer?
 
Last edited:
meano said:
Thanks for the reply. I understand this but as I don't have a value for l what do I with l in the formula to get the answer?
Click to expand...

l, the length of the wire, is the unknown whose numerical value you want to calculate.

How would you calculate the value of y in the following equation, given x = 3 and h = 5, where

h = √(x2 + y2)
 
Subhotosh Khan said:
l, the length of the wire, is the unknown whose numerical value you want to calculate.

How would you calculate the value of y in the following equation, given x = 3 and h = 5, where

h = √(x2 + y2)
Click to expand...

Don't shoot me if I'm wrong!

y = -5 + 3
y = -2

32 + -22 = 5
 
meano said:
Any chance of getting the help here?
Click to expand...
Sure we will help you, although based on what you wrote you are far behind. Can you try to do the steps that I already listed. Try one by one and well walk you through it. Those steps are listed below again. Hmm, my post does not seem to be there.

I do have a question for you.

In the equation s = sqrt 3d(l - d)/8 what exactly are you taking the sqrt of? Just the 3? Just 3d(l-d) or the whole thing?
 
Jomo said:
Sure we will help you, although based on what you wrote you are far behind. Can you try to do the steps that I already listed. Try one by one and well walk you through it. Those steps are listed below again. Hmm, my post does not seem to be there.

I do have a question for you.

In the equation s = sqrt 3d(l - d)/8 what exactly are you taking the sqrt of? Just the 3? Just 3d(l-d) or the whole thing?
Click to expand...

Thanks Jomo. It is the sqrt of the whole thing. Thing being 3d(l - d)/8.

I have done this before but when I don't use it all the time, and haven't for a while I forget. Whilst I know it is basic stuff, I just cannot remember how to do it. I could do with something to jog my memory because as soon as I see the answer I'll realise I knew how to do it all along!
 
Just looked at this again (h= 5 x = 3)

h = √(x2 + y2)

√ obviously cancels out the 2 so

h = x + y

y = h - x

y = 5 - 3

y = 2
 
meano said:
Just looked at this again (h= 5 x = 3)

h = √(x2 + y2)

√ obviously cancels out the 2 so

h = x + y

y = h - x

y = 5 - 3

y = 2
Click to expand...
oh boy! You squared the right side but you did not square the left side. If you square h you get h^2. When you square the sqrt of anything you get what is under the sqrt. That is (√(x2 + y2))^2 = x2 + y2
Consider the following: sqrt(3^2+4^2)=sqrt(9+16) = sqrt(25)=5

So sqrt(3^2+4^2)=5. Now if I square both sides I get [sqrt(3^2+4^2)]^2= 5^2 = 25

Now if we use you method on the left side we get [sqrt(3^2+4^2)]^2 =3 + 7 = 10.

But 10 does not equal 25. So one of the methods is wrong.

Again [sqrt(3^2+4^2)]^2 =(3^2+4^2). You are correct when you say that the square and sqrt cancel out but you need to cancel out the correct square and sqrt signs.

Now go back to your original problem and square both sides. Report back your results and we will go from there.
 
Ok, sorry for the delay in replying I was making something to eat.

h = √(x2 + y2)

√y = 52 - 32

√y = 25 - 9

√y = 16

y = √16

y = 4
 
Denis said:
So that means:
s = SQRT[3d(l - d) / 8]

RULE: if a = SQRT(b) then a^2 = b : remember?

Apply that and show us what you got ;)

EDIT: your last post is WRONG again...you need 2 tutors :cool:
Click to expand...

So, in my formula S = SQRT of blah blah blah. So S2 = the sum of blah blah blah? So if I solve for l, it will be l2 = blah blah blah ?
 
Last edited:
meano said:
So, in my formula S = SQRT of blah blah blah. So S2 = the sum of blah blah blah? So if I solve for l, it will be l2 = blah blah blah ?
Click to expand...
No, if you solve for I^2 then I^2 =... . But if you solve for I, the I = ...
Yes if S = sqrt( . ) the S^2 = .
Ok?
Now go and solve for S^2.
 
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