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## #1 2013-07-16 23:35:49

Agnishom
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### Trig - Help me!

Find the value of tan25°tan30°tan65°tan85°

'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'
'The whole person changes, why can't a habit?' -Alokananda

## #2 2013-07-17 03:39:56

atran
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### Re: Trig - Help me!

Start with, tan(x) = cot(90-x).

## #3 2013-07-17 11:52:22

Agnishom
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### Re: Trig - Help me!

Hmm......
I know but still tan30°tan85° remains.

'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'
'The whole person changes, why can't a habit?' -Alokananda

## #4 2013-07-17 17:35:11

SteveB
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### Re: Trig - Help me!

tan(30) is 1/(square root of 3)

Not sure what is special about Tan(85). Looks like a rather horrible irrational number even when squared.

I do notice though that the other two multiply to leave 1.
(Tan(25) * Tan(65) = 1 I presume atran's trig. result proves it. Is this because 25+65 =90 ? and Tan(90-x) * Tan(x) = 1 etc.)

I notice that the gap between 85 and 90 is only 5. This is one sixth of the gap from 30 to zero.

I can tell from calculating the answer that it is not going to give us a whole number or the square root of a whole number.
Any idea what you are supposed to be trying to prove?

I have noticed that the angles 85 + 30 + 65 = 180

The three angles are interior angles of a triangle. I am not sure where this leads or whether it is relevant.

Last edited by SteveB (2013-07-17 18:06:09)

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