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## #1 2005-04-28 02:02:43

einstein
Guest

### mathmatical formulas for trigonometry

ha ha ha ha!  u thought!!

## #2 2005-04-28 04:00:28

mathsyperson
Guest

### Re: mathmatical formulas for trigonometry

Ooh, ooh, I know one!

sin^2x + cos^2x = 1

So there!

## #3 2005-04-28 07:51:30

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

### Re: mathmatical formulas for trigonometry

Yes, I did think. But, it's not a thought allowable for this forum.

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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## #4 2005-04-29 02:52:54

Roraborealis
Member
Registered: 2005-03-17
Posts: 1,594

### Re: mathmatical formulas for trigonometry

Sin= opposite divided by hypotenuse!

That's all I know.....

School is practice for the future. Practice makes perfect. But - nobody's perfect, so why practice?

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## #5 2005-04-29 07:58:25

mathsyperson
Guest

### Re: mathmatical formulas for trigonometry

cos = adjacent divided by hypotenuse
tan = opposite divided by adjacent
tan = sin divided by cos
sec = 1 divided by cos
cosec = 1 divided by sin
cot = 1 divided by tan OR cos divided by sin

umm...

1 + cot^2x = cosec^2x
tan^2x + 1 = sec^2x

## #6 2005-04-29 10:56:29

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

### Re: mathmatical formulas for trigonometry

Hey, mathsyperson, please register and swing by every so often, you could help solve some of the visitor's problems with that knowledge.

Here is a trick to remember:  Sohcahtoa  ... sounds like an American Indian tribe, but can help you out at exams:

Sine = Opposite / Hypotenuse         (Soh...)
Cosine = Adjacent / Hypotenuse      (...cah...)
Tangent = Opposite / Adjacent         (...toa)

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

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## #7 2005-04-30 00:06:51

Roraborealis
Member
Registered: 2005-03-17
Posts: 1,594

### Re: mathmatical formulas for trigonometry

When do you learn this?

School is practice for the future. Practice makes perfect. But - nobody's perfect, so why practice?

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## #8 2005-05-02 08:32:34

Mr T
Member
Registered: 2005-03-30
Posts: 1,012

### Re: mathmatical formulas for trigonometry

i knew that one.

I come back stronger than a powered-up Pac-Man
I bought a large popcorn @ the cinema the other day, it was pretty big...some might even say it was "large
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## #9 2005-06-13 06:50:48

Doggy
Guest

### Re: mathmatical formulas for trigonometry

cos x/2=?
sin x/2=?

btw
sin(x+/-y)=sin^x ^ cos^y +/- cos^x ^ sin^y

## #10 2005-06-13 08:14:53

mathsyperson
Guest

### Re: mathmatical formulas for trigonometry

Not sure if this is what you wanted but...

sin^2(x/2) = (1-cos x)/2
cos^2(x/2) = (1+cos x)/2

I think to get half angles like that you can substitute in cos x and then square root what you get.

## #11 2005-06-13 10:38:53

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

### Re: mathmatical formulas for trigonometry

sin (x/2) = ± sqrt[ (1 - cos x) / 2 ]

cos (x/2) = ± sqrt[ (1 + cos x) / 2 ]

(This is exactly what mathsyperson had, just with a square root applied)

The "±" means that you need to provide your own + or - depending on where the angle points.

... and there are lots more "trigonometric identities" ... too many for me to remember ... I had to look this one up.

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

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## #12 2005-06-17 09:35:16

NIH
Member
Registered: 2005-06-14
Posts: 33

### Re: mathmatical formulas for trigonometry

In a non-right angled triangle, with internal angles a, b, c, tan a + tan b + tan c = tan a * tan b * tan c.

2 + 2 = 5, for large values of 2.

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