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## #1 2005-07-23 23:10:22

GurraTedden
Member
Registered: 2005-07-20
Posts: 19

### Angle equation

Hi.
How do I solve sin(θ) = 0.38cos(θ) ???

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## #2 2005-07-23 23:14:32

MathsIsFun
Registered: 2005-01-21
Posts: 7,659

### Re: Angle equation

I remember my trig using "SOHCAHTOA" (see http://www.mathsisfun.com/sine-cosine-tangent.html)

Therefore tan θ = sin θ / cos θ

So: sin(θ)/cos(θ) = 0.38 = tan θ

And: θ = tan-¹ 0.38 = 20.8°

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #3 2005-07-23 23:17:40

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

### Re: Angle equation

Divide both sides by cosθ: sinθ/cosθ=0.38
Simplify left-hand side: tanθ=0.38
Take arctans: θ=tan-¹(0.38)=20.8° to 1 decimal place

Why did the vector cross the road?
It wanted to be normal.

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## #4 2005-07-23 23:19:36

MathsIsFun
Registered: 2005-01-21
Posts: 7,659

### Re: Angle equation

SNAP

(Looking at the times, I must be slower at finishing my posts)

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #5 2005-07-23 23:37:30

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

### Re: Angle equation

You can time how long it takes people to post?
That's extremely cool/pointless.

Why did the vector cross the road?
It wanted to be normal.

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## #6 2005-07-24 00:00:01

MathsIsFun
Registered: 2005-01-21
Posts: 7,659

### Re: Angle equation

No, not really, though that is an interesting idea. It just seemed to me that there were 3 minutes difference between our posts, but I started first, but  . . .  oh, I don't know!

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #7 2005-07-24 00:23:28

Zach
Member
Registered: 2005-03-23
Posts: 2,075

### Re: Angle equation

Failure.

Boy let me tell you what:
I bet you didn't know it, but I'm a fiddle player too.
And if you'd care to take a dare, I'll make a bet with you.

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## #8 2005-07-27 21:43:10

Nitrofu
Guest

### Re: Angle equation

the 3d .obj reader i have at http://www15.brinkster.com/nitrofurano/sdlbasic/ uses this

(i needed to rotate the viewer over the landscape, and for this i need to know the angle)

(this is simple to do as code, i don't know math notations as well...)

## #9 2005-07-27 21:46:40

Nitrofu
Guest

### Re: Angle equation

the problem starts when (using arcsin, arccos and arctan) you need to know the quadrant for angles larger than 90degrees (afaik)