# Question about the meaning of the Δi term in this equation

new90
Homework Statement:
question
Relevant Equations:
n
∑ficosΔi = 0 what is the meaning of Δi

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Homework Statement:: question
Relevant Equations:: n

∑ficosΔi = 0 what is the meaning of Δi
This doesn't look so much like a homework problem, but more of a conceptual question?

Also, can you please show us where you got this equation? Can you maybe post a screenshot of it, or attach a picture of it? Since you did not post it in LaTeX, it's hard to interpret what it is for. Thanks.

new90
but the thing i want to know what ddoes it means Δi

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Without context and further specification: an angle.

but the thing i want to know what ddoes it means Δi
Still an angle.

new90
ok

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but the thing i want to know what ddoes it means Δi
The exact format is important. Is it ##\Sigma f_i\cos(\Delta i)## or ##\Sigma f_i\cos(\Delta_i)##?
What is the subject matter? What preceding references to ##\Delta## or ##\Delta i## or ##\Delta_i## in the text?

berkeman
Without context anything can be any other thing. In mathematical and physical contexts ##\Delta## generally stands for difference (usually very small one ) or a very small quantity of something. And ##i## is a dummy variable (generally).

Without context anything can be any other thing. In mathematical and physical contexts ##\Delta## generally stands for difference (usually very small one ) or a very small quantity of something. And ##i## is a dummy variable (generally).

I'm not sure about the 'very small' part. For infinitesimal changes we might use the little 'd'. But I see no reason why not to use ##\Delta## even if the change is very large - as far as I'm aware it's just a change, the bog standard "final - initial". We could apply a force to something, wait 10 years and measure its ##\Delta E_k##.

Please do correct me if I've misinterpreted something!

I'm not sure about the 'very small' part. For infinitesimal changes we might use the little 'd'. But I see no reason why not to use ##\Delta## even if the change is very large - as far as I'm aware it's just a change, the bog standard "final - initial".

Please do correct me if I've misinterpreted something!
You see this ##\Delta## once caused me a serious problem during my reading of Feynman Lectures on Physics, in volume 1 of FLP you will find ##\Delta## being used for small changes, however, other books tend to write ##\delta## for small changes.

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etotheipi
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I'm not sure about the 'very small' part. For infinitesimal changes we might use the little 'd'. But I see no reason why not to use ##\Delta## even if the change is very large - as far as I'm aware it's just a change, the bog standard "final - initial". We could apply a force to something, wait 10 years and measure its ##\Delta E_k##.

Please do correct me if I've misinterpreted something!
Delta small is a very physical point of view. In other areas as mathematics or economy it is normally just any difference, often a step width.

But "i" could be anything: imaginary unit, index or variable.

etotheipi
You see this ##\Delta## once caused be a serious problem during my reading of Feynman Lectures on Physics, in volume 1 of FLP you will find ##\Delta## being used for small changes, however, other books tend to write ##\delta## for small changes.

I've just looked and you're quite right! That is awfully confusing!

I guess I'm just used to seeing ##\Delta## for a finite change, ##\delta## for a very small variation and ##d## for an infinitesimal change. But as @fresh_42 mentioned, usage amongst many different people can be very inconsistent!