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# prooooovin intrinsic blah blahs watch

1. okay. this is probably a crazy question, but how the flip am I meant to show that:

ds/d psi = cosec psi

given that

s = ln (tan psi/2)

Boo hoo hoo...
2. differentiate ??
3. (Original post by lesser weevil)
okay. this is probably a crazy question, but how the flip am I meant to show that:

ds/d psi = cosec psi

given that

s = ln (tan psi/2)

Boo hoo hoo...
Some people post without thinking (spam!!)
4. Just a case of pre-exam nerves, methinks.

Don't worry, nobody's too fond of intrinsic. But there's pretty much a set method for all the questions...
5. s = ln(tan (psi/2))

ds/dpsi = sec²(psi/2) / 2tan(psi/2)

= 1 / 2sin(psi/2)cos(psi/2)

2sin(psi/2)cos(psi/2) = sin(psi)

.'. ds/d psi = 1/sin(psi) = cosec(psi)

QED
6. thanks.

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