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**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,137

Hello everyone,

I need help with trigonometric equations, a link to math is fun would be great. But first, could anyone help me with this question? A step-by-step answer would be great. Thanks in advance.

Solve the following trigonometric equations for

(edited)

*Last edited by David (2014-06-06 03:56:39)*

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

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First, you've to transform this into an equation of sines. Then, apply the submultiple angle formulae.

I'll do this once I am back from the bookstore.

'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'

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**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,137

ty

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

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**liuv****Member**- Registered: 2006-05-14
- Posts: 29

I'm from Beijing China.

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Please post the answer that you originally attached with the first post.

I'm not sure if you want a numerical solution or an exact one.

'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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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

The 300° is just an approximation is it not?

**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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How did he get 75 there?

'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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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

I am not sure, but he should replace the = with ≈ in his work.

**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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**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,137

Wait, I will upload a image.

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

That says 1 / 2 not 1 / 4.

**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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**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,137

oops...

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,322

using edited version

cos (x/2) = 1/4

Cos2A = 2.cos^2 (A) -1

cos(x) = 2 x (1/4)^2 - 1 = - 7/8

then use acos

Bob

*Last edited by bob bundy (2014-06-06 04:02:02)*

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Does using acos give you any exact value?

'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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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,322

no. I don't think you can get an exact value easily here.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,137

Could you explain a little bit? ty.

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,322

sec = 1/cos so invert the equation.

Then use the double angle formula:

The rest is arithmetic.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**David****Member**- From: Bumpkinland
- Registered: 2014-04-23
- Posts: 3,137

Thanks Bob and everyone. Is the double angle formula on mif?

Meaningless, meaningless, Everything is meaningless! - Ecclesiastes 1:2

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The double angle formula can be derived with the compound angle formula

'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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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,322

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,322

Off-line for a while. I'll be back.

B

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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These identities are a pain.

'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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**liuv****Member**- Registered: 2006-05-14
- Posts: 29

bobbym wrote:

The 300° is just an approximation is it not?

I'm from Beijing China.

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