Sorry your browser is not supported!

You are using an outdated browser that does not support modern web technologies, in order to use this site please update to a new browser.

Browsers supported include Chrome, FireFox, Safari, Opera, Internet Explorer 10+ or Microsoft Edge.

Geek Culture / Simple Math

Author
Message
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 15th Apr 2005 11:59
Link
Well I am taking what most people would consider an extremely easy math course, so I need some help with a problem.



First, I forgot the Law of Cosines, so I can't do much without that.

Secondly, I am completely clueless when it comes to re-organizing formulas in mathematics. Im sure it's very simple, but math was never my strength, so any help would be appreciated. Please if you are going to post the answer, could you explain to me how you arranged it so I know?

Thanks alot,
-Apolloed
Back to top
Profile PM Email Website
kenmo2
19
Years of Service
User Offline
Joined: 15th Apr 2005
Location:
Posted: 15th Apr 2005 12:20
Link
Well the original formula is (one form of it...)

C^2 = A^2 + B^2 - 2ABcosC

Add 2ABcosC and subtract C^2...

2ABcosC = A^2 + B^2 - C^2

Divide by A and B (or, AB)...

2cosC = A/B + B/A - C^2/AB

And divide by 2...

cosC = A/2B + B/2A - C^2/2AB

Which can be written many ways, such as

cosC = (1/2)(A/B) + (1/2)(B/A) + (1/2)(C^2/AB)

Etc. That should help quite a bit.
Back to top
Profile PM
Richard Davey
Retired Moderator
22
Years of Service
User Offline
Joined: 30th Apr 2002
Location: On the Jupiter Probe
Posted: 15th Apr 2005 12:27 Edited at: 15th Apr 2005 12:29
Link
Whoa.. trig flashback! The law of cosines is calculating one side of a triangle when the opposite angle and the other sides are known.

a(sq) = b(sq) + c(sq) - 2bccosA

(A being the top point of your triangle, B lower left, C lower right, a base, c left diagnol, b right diagnol)

edit: use Kenmos calcs above

Two Worlds and in Between
Hot Metal and Methedrine
Back to top
Profile PM Email Website
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 15th Apr 2005 12:30
Link
Ah, ok, Thanks for all the help
Back to top
Profile PM Email Website
kenmo2
19
Years of Service
User Offline
Joined: 15th Apr 2005
Location:
Posted: 15th Apr 2005 12:32
Link
Uh, that last line I wrote should be:

cosC = (1/2)(A/B) + (1/2)(B/A) - (1/2)(C^2/AB)

(with a - not a +.) For some reason I can't edit the post.
Back to top
Profile PM
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 27th Apr 2005 12:27 Edited at: 27th Apr 2005 12:30
Link
How Would I Go About Solving This Problem...I need to find the length of the side with a question mark, could someone please explain?



Thanks,
Apolloed

Digitalmodr
Coder_David
[Apolloed ]

Attachments

Login to view attachments
Back to top
Profile PM Email Website
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 27th Apr 2005 12:39
Link
Ok, I think im starting to get this, I got:

35.045...

is this correct?

Digitalmodr
Coder_David
[Apolloed ]
Back to top
Profile PM Email Website
bitJericho
22
Years of Service
User Offline
Joined: 9th Oct 2002
Location: United States
Posted: 27th Apr 2005 13:39
Link
uh.. its quite easy to check...

isn't it like..

a^2 * b^2 = c^2

Or something like that...


Yarr join teh New and Improved LoGD!
Back to top
Profile PM Email Website
David T
Retired Moderator
22
Years of Service
User Offline
Joined: 27th Aug 2002
Location: England
Posted: 27th Apr 2005 16:50 Edited at: 27th Apr 2005 16:52
Link
No - not for the above problem. A right handed triangle uses pythagoras:

sum of the squares of two sides = square of hypotenuese

For that problem you'd need to use the cosine rule, as posted above. A woudl be 10 degrees, B and C would be 90 and 120.

Facts are meaningless.
You could use facts to prove anything that's even remotely true.
Back to top
Profile PM Email Website
bitJericho
22
Years of Service
User Offline
Joined: 9th Oct 2002
Location: United States
Posted: 27th Apr 2005 16:59
Link
ahh I see... It's been years since I've done this stuff, and even then I didnt' get a good grasp of it


Yarr join teh New and Improved LoGD!
Back to top
Profile PM Email Website
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 27th Apr 2005 20:13
Link
So the third side should be about 35ft?

Digitalmodr
Coder_David
[Apolloed ]
Back to top
Profile PM Email Website
Fallout
22
Years of Service
User Offline
Joined: 1st Sep 2002
Location: Basingstoke, England
Posted: 28th Apr 2005 00:38
Link
This post is a testament to DB! There're so many people who have no concept of trig, which is a fundamental part of 3D, but everyone is still making games. How cool is that?

Back to top
Profile PM
Megaton Cat
21
Years of Service
User Offline
Joined: 24th Aug 2003
Location: Toronto, Canada
Posted: 28th Apr 2005 01:46
Link
What's even scarier is I don't understand a thing being discussed in this thread.

My cat! My cat is on fire! Dear god someone help!
Back to top
Profile PM Email Website
Dodo
20
Years of Service
User Offline
Joined: 8th Aug 2004
Location: eating lunch
Posted: 28th Apr 2005 06:33 Edited at: 28th Apr 2005 06:34
Link
for the above problem, you would substitute in the values to the cosine rule, like this:

(x)^2=(90)^2+(120)^2-2(90)(120)cos(10)

then, for this problem at least, you can just sqaure root both sides like this:

x=(sqrt)(90^2+120^2-2(90)(120)cos(10))

and type that all onto your calculator to get about 35ft

@Apolloed - yes, that is correct

Part of solving the problem is actually noticing that the problem is there in the first place

Back to top
Profile PM Email Website
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 28th Apr 2005 06:47
Link
Next thing...how do i get the inverse sine or inverse cosine without a calculator? i can do sine and cosine, but how do you get their inverses?

Digitalmodr
Coder_David
[Apolloed ]
Back to top
Profile PM Email Website
David T
Retired Moderator
22
Years of Service
User Offline
Joined: 27th Aug 2002
Location: England
Posted: 28th Apr 2005 08:28 Edited at: 28th Apr 2005 08:29
Link
Without? Wow - I'm surprised you managed to calc sine and cosine without a calculator. That's an awfully long formula

I don't know whether you actually want the formula or just worded it wrong, but the inverse allows you get get an angle in a triangle.

Say you have sides A and H which are 10 and 30 respectively.

You can say angle theta, which is adjacent to 10, is X.

Cos X = adj / hyp
Cos X = 10/30

to get an angle out of a cosine value, then use cos-1:

cos-1(10/30) = X

Facts are meaningless.
You could use facts to prove anything that's even remotely true.
Back to top
Profile PM Email Website
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 28th Apr 2005 08:31
Link
I understand that...but how do i do cos-1 ? Like cos = adj / hyp

How do i get the inverse? other than typing cos-1 into a calc?

Digitalmodr
Coder_David
[Apolloed ]
Back to top
Profile PM Email Website
David T
Retired Moderator
22
Years of Service
User Offline
Joined: 27th Aug 2002
Location: England
Posted: 28th Apr 2005 08:33
Link
You don't - cos-1 is purely reversing a cos.

So

cos-1 ( cos(45) ) results in 45. It takes a cos value and converts it into an angle.

Facts are meaningless.
You could use facts to prove anything that's even remotely true.
Back to top
Profile PM Email Website
Ace Of Spades
19
Years of Service
User Offline
Joined: 6th Mar 2005
Location: Across the ocean
Posted: 28th Apr 2005 08:35 Edited at: 28th Apr 2005 08:35
Link
Yes, i know what it does...but How does it do it? It doesn't have every single millionth of a degree programmed into the calculator. So when you do the inverse of cos on a calculator, what math does it perform?

Basically, how do you reverse the cos?

Digitalmodr
Coder_David
[Apolloed ]
Back to top
Profile PM Email Website
indi
22
Years of Service
User Offline
Joined: 26th Aug 2002
Location: Earth, Brisbane, Australia
Posted: 28th Apr 2005 15:51
Link
get your free homework done at the game creators website forum joke intended under the reality of my words
if you had TGC forums at work you could get paid to work via proxy minds, scary thought

If no-one gives your an answer to a question you have asked, consider:- Is your question clear.- Did you ask nicely.- Are you showing any effort to solve the problem yourself
Back to top
Profile PM Email
Dodo
20
Years of Service
User Offline
Joined: 8th Aug 2004
Location: eating lunch
Posted: 29th Apr 2005 02:33
Link
I really want to know why you can't do it on a calculator...

but if you are programming a calculator for the computer then it is often referred to as arccosine in most programming languages, the command acos in DB

Part of solving the problem is actually noticing that the problem is there in the first place

Back to top
Profile PM Email Website
David T
Retired Moderator
22
Years of Service
User Offline
Joined: 27th Aug 2002
Location: England
Posted: 29th Apr 2005 04:21
Link
Quote: "Yes, i know what it does...but How does it do it? It doesn't have every single millionth of a degree programmed into the calculator. So when you do the inverse of cos on a calculator, what math does it perform?"


You know how sine is done? The formula goes on forever I believe, and its highly likely arcsine is the same.

Actually just searched on google, now, don't know why you couldn't have done the same

Found under the oh-so-cryptic keywords of "sine formula" and "arcsine formula"

http://mathworld.wolfram.com/WallisSineFormula.html

http://www.math.duke.edu/education/ccp/materials/intcalc/inverse/inverse3.html

Its not some simple scale factor job, finding arcsine

Facts are meaningless.
You could use facts to prove anything that's even remotely true.
Back to top
Profile PM Email Website
Sarge
19
Years of Service
User Offline
Joined: 3rd May 2005
Location: Battle Creek, Michigan
Posted: 4th May 2005 16:06
Link
Here's a little something I did up real quick to answer you trig question. I followed it through to solve for all of the angles and sides using law of cosines and law of sines. Hope it helps. I love math!!

Attachments

Login to view attachments
Back to top
Profile PM
Back to top

Login to post a reply

Server time is: 2024-11-15 01:01:03
Your offset time is: 2024-11-15 01:01:03