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# deltaT to dT watch

1. http://www.thestudentroom.co.uk/show...4&postcount=18

deltT / [2tan(deltpsi/2)] = T mu

Finally we let A and B get close together, so that deltT and deltpsi become small:

dT/d(psi) = T mu
i dont get how if deltT and deltpsi become small then the equation reduces to dT/d(psi)
2. For small angles x (in radians), tanx is approximately x.
3. so then how comes its d(psi) and not 2d(psi) then? still doesnt make sense to me
so then how comes its d(psi) and not 2d(psi) then? still doesnt make sense to me
Look at the series expansion of 2tan(x/2).

You get:

2tan(x/2) = x + (x^3)/12 + (x^5)/120 + ...

So as for small value of x, 2tan(x/2) ~=~ x

That is why the expression becomes dT/d(psi).

Euclid
5. ah ok thanx alot!
so then how comes its d(psi) and not 2d(psi) then? still doesnt make sense to me
cos the 2s cancel.

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Updated: January 8, 2005
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