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#1 2015-07-04 06:00:25
Weird Equations from Physics Problems
A lens with a focal length of 16 cm produces a sharp image of an object in two positions, which are 60m apart from each other. Find the distance between the screen and the object.
This might seem a little stupid, but I am having some trouble solving the following equations:
Obviously, Mathematica gives:
In[92]:= Solve[{16 d == x (d - x),
16 d == (x + 60) (d - (x + 60))}, {x, d}]
Out[92]= {{x -> -48, d -> -36}, {x -> 20, d -> 100}}What is a simple way to do this by hand?
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
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#2 2015-07-04 08:57:06
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Weird Equations from Physics Problems
Eliminate x and solve
or eliminate d and solve,
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#3 2015-07-04 13:32:04
Re: Weird Equations from Physics Problems
Thanks, how did shopping go?
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
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#4 2015-07-04 13:41:50
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Weird Equations from Physics Problems
Got caught in a big storm.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#5 2015-07-04 14:10:25
Re: Weird Equations from Physics Problems
Did you land up on a deserted island?
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
Offline
#6 2015-07-04 15:11:34
Re: Weird Equations from Physics Problems
Eliminate x and solve
or eliminate d and solve,
I would not need x, see the problem statement.
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
Offline
#7 2015-07-04 16:13:46
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Weird Equations from Physics Problems
An quadratic is provided for both.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
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