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

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: ashwinkandel on April 27, 2011, 04:40:53 pm

Title: Trigonometry Problem
Post by: ashwinkandel on April 27, 2011, 04:40:53 pm

I just came to one problem of trigonometry. Solved it and looked the marking scheme , but my answer didn't matched and i did not understand the process given in marking scheme. the question paper has been attached below and the question no. is 12. It would be great help if someone can clarify me very soon(with in few hours) as because tomorrow i have got my test of mathematics.

Title: Re: Trigonometry Problem
Post by: EMO123 on April 27, 2011, 04:49:43 pm

excuse me there is no Q no. 12 in this paper  >:(

Title: Re: Trigonometry Problem
Post by: ashwinkandel on April 27, 2011, 05:00:11 pm

I am sorry, it was question no. 11.  :)

Title: Re: Trigonometry Problem
Post by: Vin on April 27, 2011, 05:07:00 pm

a)
3 (2 sin x - cos x) = 2 (sin x - 3 cos x)
6 sin x - 3 cos x = 2 sin x - 6 cos x
6 sin x - 2 sin x = -6 cox s + 3 cos x
4 sin x = -3 cos x

sin x      -3
----  =   ---
cos x      4

sin x/ cos x = tan x.

tan x = -3/4

b) for this you have multiple methods.
I do it this way.

x = tan^-1 (3/4)
(neglecting the sign)

x = 36.9

tan x is negative, so it lies in the 2nd and the 4th quadrant . (check the attachment )

x1 = 180 - 36.9
= 143.1

x2  = 360 - 36.9
= 323.1

Given domain is 0 to 360 so your two values are 143.1 and 323.1

Wait, now I typed all of it, is it Q.11 or Q1. ii) ?
-.-

Title: Re: Trigonometry Problem
Post by: ashwinkandel on April 27, 2011, 05:14:29 pm

It's question no. 11  ;D

Title: Re: Trigonometry Problem
Post by: EMO123 on April 27, 2011, 05:16:39 pm

vin it's incorrect but well tried

11.(a)

f(x)=2
:. 4-3sin x=2
   3sin x= 2
   sin x=2/3

therefore x=sin^-12/3   (keep your calculator in radians mode)
             x=0.729
 :)

Title: Re: Trigonometry Problem
Post by: ashwinkandel on April 27, 2011, 05:22:05 pm

thanks EMO123 , but can you do remaining part of number 11 plz.

Title: Re: Trigonometry Problem
Post by: Vin on April 27, 2011, 07:46:51 pm

Quote from: EMO123 on April 27, 2011, 05:16:39 pm

vin it's incorrect but well tried

11.(a)

f(x)=2
:. 4-3sin x=2
   3sin x= 2
   sin x=2/3

therefore x=sin^-12/3   (keep your calculator in radians mode)
             x=0.729
 :)

How come?

Title: Re: Trigonometry Problem
Post by: EMO123 on April 28, 2011, 02:23:58 pm

Quote from: Vin on April 27, 2011, 07:46:51 pm

How come?

this is the paper of cie as levels Paper 12 chek it vin

but still
11 (a)

as given in question f(x)=2 and the Funtion is f:-->4-3sin x(can also be written as f(x)=4-3sin x you must be knowing this but still)
so therefore substitute and get you answers

Title: Re: Trigonometry Problem
Post by: EMO123 on April 28, 2011, 02:29:27 pm

11(b)
sketch the graph
by y=f(x)
so f(x)= 0, 1/2pie, pie, 3/2pie, 2pie
and find y and sketch the graph

Title: Re: Trigonometry Problem
Post by: Vin on April 28, 2011, 02:43:45 pm

Quote from: EMO123 on April 28, 2011, 02:23:58 pm

this is the paper of cie as levels Paper 12 chek it vin

Yeah, but nothing's wrong with my solution, right? :P

Title: Re: Trigonometry Problem
Post by: EMO123 on April 28, 2011, 02:51:24 pm

Quote from: Vin on April 28, 2011, 02:43:45 pm

Yeah, but nothing's wrong with my solution, right? :P

vin you may e right but i think you are doing another question paper download which uploaded by ashwinkandel