IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: coolcar221 on October 06, 2009, 11:35:13 pm

Title: Trig question
Post by: coolcar221 on October 06, 2009, 11:35:13 pm: Show that the equation 2tan²xcosx=3 can be written in the form 2cos²x+3cosx-2=0
Title: Re: Trig question
Post by: nid404 on October 07, 2009, 07:57:24 am: will answer when I'm back from my classes
Title: Re: Trig question
Post by: astarmathsandphysics on October 07, 2009, 09:31:36 am: Quote from: coolcar221 on October 06, 2009, 11:35:13 pm
Show that the equation 2 tan2x cosx = 3 can be written in the form 2 cos2x + 3cosx - 2 = 0
Can you check the question?
Title: Re: Trig question
Post by: nid404 on October 07, 2009, 09:34:42 am: i was wondering.....yes can u please check the question again
Title: Re: Trig question
Post by: cel on October 07, 2009, 03:33:27 pm: hi..
u jst have to substitute tan²x=sec²x in the eqn
Title: Re: Trig question
Post by: astarmathsandphysics on October 07, 2009, 03:50:05 pm: Tan2x is not equal to sec2x
Title: Re: Trig question
Post by: Ghost Of Highbury on October 07, 2009, 03:50:52 pm: lol..:P
Title: Re: Trig question
Post by: Eamyzz on October 07, 2009, 04:12:06 pm: hey all ;D ;D ;D
Title: Re: Trig question
Post by: Ghost Of Highbury on October 07, 2009, 04:13:56 pm: hey eamyz!
welcome back!
wrong topic though...:P

try posting in the chit chat sectin...u'll be welcomed with warm hands!!!!
Title: Re: Trig question
Post by: Eamyzz on October 07, 2009, 04:15:48 pm: hahahahaa....i no i couldnt resist nt writing ;D ;D ;D
Title: Re: Trig question
Post by: Eamyzz on October 07, 2009, 04:23:36 pm: wat is sec2x ???
Title: Re: Trig question
Post by: Ghost Of Highbury on October 07, 2009, 04:35:05 pm: sec^2 x = (1/cos^2x)
Title: Re: Trig question
Post by: Eamyzz on October 07, 2009, 04:36:48 pm: Quote from: eddie_adi619 on October 07, 2009, 04:35:05 pm
sec^2 x = (1/cos^2x)

is this hw u write it here or its written like this evrywhere??
Title: Re: Trig question
Post by: Ghost Of Highbury on October 07, 2009, 05:05:38 pm: huh?
didnt get u?
Title: Re: Trig question
Post by: astarmathsandphysics on October 07, 2009, 05:25:41 pm: That equation for sec^2x is right
Title: Re: Trig question
Post by: Eamyzz on October 08, 2009, 12:50:01 am: u wont get me i mean that in da exam can they wite it in this form or u guys r just abreviating it ???
Title: Re: Trig question
Post by: cel on October 09, 2009, 03:49:37 pm: sry..it's tan²x=sec²x-1
Title: Re: Trig question
Post by: Eamyzz on October 14, 2009, 02:06:00 am: Quote from: cel on October 09, 2009, 03:49:37 pm
sry..it's tan²x=sec²x-1

huh???
dnt get ur pt
Title: Re: Trig question
Post by: Ghost Of Highbury on October 14, 2009, 06:43:50 am: Quote from: Eamyzz on October 14, 2009, 02:06:00 am

huh???
dnt get ur pt

its a formula he suggested to be used in the first Q..
Title: Re: Trig question
Post by: nid404 on October 14, 2009, 08:22:32 am: ok from what I did

2tan²xcosx=3

2tan²x=2sin²x/ 2cos²x

substituting u get
2sin²x/ 2cos²x X cosx =3
2sin²x/2cosx=3
sin²x/cosx=3

sin²x=1-cos²x

1-cos²x/cosx=3
1-cos²x=3cosx
3cosx+cos²x-1=0

check the question again plzz
Title: Re: Trig question
Post by: Ghost Of Highbury on October 14, 2009, 08:35:00 am: @nid - 2tan²x = 2sin²x/cos²x not 2sin²x/2cos²x

1) 2tan²x cos x = 3

first simplify this to..

2sin²x/cos x = 3

cross multiply to get

3 cos x = 2sin²x
3cos x - 2sin²x = 0

-2 sin²x = 2cos²x - 2

so it becomes... 3cos x + 2cos²x -2 =0

hence proved..
Title: Re: Trig question
Post by: nid404 on October 14, 2009, 08:38:52 am: oh yes....no wonder.....silly error
ho gaya....question solved
Title: Re: Trig question
Post by: Eamyzz on October 14, 2009, 04:42:48 pm: Quote from: Eamyzz on October 14, 2009, 02:06:00 am

huh???
dnt get ur pt

oooooh gt it :-[ ::)
Thanks