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#1 2007-02-04 23:38:27
- Toast
- Real Member
- Registered: 2006-10-08
- Posts: 1,321
Some formulae
Simple rearranging here, but I think I mighta made a mistake (or two)
Solve for s:
...
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#2 2007-02-05 01:34:15
- mathsyperson
- Moderator
- Registered: 2005-06-22
- Posts: 4,900
Re: Some formulae
You went wrong in the step when you multiplied everything by s. The last term should just be cr, not crs.
If you follow through from there then you get:
rsv = cs - cr
rsv - cs = -cr
s(rv-c) = -cr
s = cr/(c-rv)
Why did the vector cross the road?
It wanted to be normal.
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#3 2007-02-05 21:41:35
- Dross
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- Registered: 2006-08-24
- Posts: 325
Re: Some formulae
Toast wrote:
Solve for s:
...
I think it's worth noting what you've done in the last three steps - as soon as you get to the step:
you've divided through by
and decided that - but remember that you always have to be sure you're not dividing by zero. However, because , then or (or both) - but you can't conclude either one of them is zero until you know for sure that they're both zero, or that one of them is not zero (for example, if you know s is always positive).See what I'm saying?
Bad speling makes me [sic]
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#4 2007-02-06 00:36:01
- Toast
- Real Member
- Registered: 2006-10-08
- Posts: 1,321
Re: Some formulae
Ah, yep, thanks both. If I divide through it'll be no use for quadratics ;o
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