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Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: masterof13 on May 25, 2010, 01:19:22 pm

Title: doubt in finding angles!
Post by: masterof13 on May 25, 2010, 01:19:22 pm: i have a huge problem when it comes to finding the second angle of an equation like this for eg cos(x-73.4)=3/5 ???
the first angle is easy to find but i really need help to find the second angle, can anyone give me a step by step solution?
thanks alot!!!
masterof13
Title: Re: doubt in finding angles!
Post by: falafail on May 25, 2010, 01:34:38 pm: Quote from: masterof13 on May 25, 2010, 01:19:22 pm
i have a huge problem when it comes to finding the second angle of an equation like this for eg cos(x-73.4)=3/5 ???
the first angle is easy to find but i really need help to find the second angle, can anyone give me a step by step solution?
thanks alot!!!
masterof13
well at first you obviously have to cos^-1 3/5, so you get an angle right?
since this is cosine and +ve, you also do 360 - the angle

remember, CAST
(http://www.mathsrevision.net/alevel/pure/unitcircle3.gif)
in the first quadrant, sin cosine and tan are all +ve.
in teh second quadrant, sin only is +ve. (you do 180 - the angle)
in the third quadrant, tan only is +ve. (180 + the angle)
in the fourth quadrant, cos only is +ve. (360 - the angle)

so if you get a +ve angle with sin for example, your answer would be that angle, and 180 - the angle.
if you get a +ve angle with tan, your answer would be that angle, and 180 + the angle.

also, any angle + 360 is the same angle, but usually you don't have to do that because it's not in the range.

i hope this helps. feel free to ask me if you still have any questions. :)
Title: Re: doubt in finding angles!
Post by: masterof13 on May 25, 2010, 01:38:45 pm: WOW!! Thanks this helped so much!!
i actually forgot the CAST rule!!
thank you very very much!! ;D
Title: Re: doubt in finding angles!
Post by: falafail on May 25, 2010, 04:21:53 pm: Quote from: masterof13 on May 25, 2010, 01:38:45 pm
WOW!! Thanks this helped so much!!
i actually forgot the CAST rule!!
thank you very very much!! ;D

you're welcome :)
Title: Re: doubt in finding angles!
Post by: dodo on June 08, 2010, 03:36:41 pm: plzzzzzzzzzzzzzzzzz hlep question 9 in jan 2010 part a pllzzzzzzzzzzzzzzzzzzzzzzzzz how to get x from 6x^-0)5 -3/2x^0)5 plzzzzzzzzzzzzzzzzzzzzzzzzzzzz
Title: Re: doubt in finding angles!
Post by: dodo on June 08, 2010, 03:44:01 pm: sorry its 6x^-0.5-3/2x^0.5 =0 how 2 get x from this equ .
Title: Re: doubt in finding angles!
Post by: Ghost Of Highbury on June 08, 2010, 03:48:42 pm: Quote from: dodo on June 08, 2010, 03:44:01 pm
sorry its 6x^-0.5-3/2x^0.5 =0 how 2 get x from this equ .

use brackets to indicate exactly what the question is.

Provide paper/ms links

Give all details about the paper, including board, year, session, paper no.
Title: Re: doubt in finding angles!
Post by: dodo on June 08, 2010, 03:53:09 pm: its paper c2 jan2010 question 9 part a
plzzzzzzzzzzzzzzzzzzzzz hlep
Title: Re: doubt in finding angles!
Post by: Ghost Of Highbury on June 08, 2010, 04:06:06 pm: Quote from: dodo on June 08, 2010, 03:53:09 pm
its paper c2 jan2010 question 9 part a
plzzzzzzzzzzzzzzzzzzzzz hlep

POST THE LINK PLEASE.
Title: Re: doubt in finding angles!
Post by: dodo on June 08, 2010, 04:33:10 pm: i don't have the link one of my friends give it 2 u sorrrrry
Title: Re: doubt in finding angles!
Post by: AcidicTastebuds on June 08, 2010, 06:15:51 pm: How do you work the cast rule in the main angle is negative?