| Author |
 Topic  |
|
|
jfg4707
Average Member
USA
19 Posts |
 Posted - 10/05/2007 : 21:33:32
|
Hi,
I am trying to solve a trigonometry equation, but I keep getting the wrong answer. I can't figure out what I am doing wrong.
Problem
Find all solution for the following equation on the interval 0 x2 : 5cos(x+3)=1.
Solution
5cos(x+3)=1
cos(x+3)=1/5
x+3=arccos(1/5)=1.369
x=1.369-3=-1.125
The reference angle of -1.125 is 1.125. So,
x=1.125 and 2-1.125=5.158.
The correct answers are 1/914 amd 4.653
Thank you for any help you can give me. |
 |
|
|
tkhunny
Advanced Member
USA
1001 Posts |
Posted - 10/05/2007 : 21:49:25
|
1.369 - 3 = -1.631 NOT -1.125
-1.631 + 2 = 4.653
You find the other one.
(Typo Repaired - Thanks uberclay. How did I get 4.653 right?) |
Edited by - tkhunny on 10/06/2007 01:14:39 |
|
|
|
uberclay
Advanced Member
Canada
159 Posts |
Posted - 10/06/2007 : 00:03:52
|
quote:
Originally posted by tkhunny
1.369 - 3 = -1.631 NOT -1.125
|
|
|
|
jfg4707
Average Member
USA
19 Posts |
Posted - 10/06/2007 : 01:15:52
|
tkhunny,
With x = 4.653, a third quadrant angle, I assumed that the second angle must be in Quadrant 2, so they would have the same sign when cosine was applied; and it is in Quadrant II, i.e., x = 1.914. But I have not been able to derive 1.914.
I thought that finding the reference angle of 4.653 and then stubracting it from would give me the correct answer, but it does not: 4.653-=1.511 and -1.511=1.631. Everything else I have tried fails to produce 1.914. Can you explain to me what I shoulld be doing?
Thank you |
|
|
|
skeeter
Advanced Member
USA
5634 Posts |
Posted - 10/06/2007 : 09:01:03
|
arccos(1/5) = 1.369, a quad I angle.
x = 1.3694 - 3 = -1.631
arccos(1/5) = 2 - arccos(1/5) = 4.914, a quad IV angle.
x = 4.914 - 3 = 1.914 |
|
|
|
jfg4707
Average Member
USA
19 Posts |
Posted - 10/06/2007 : 13:27:54
|
| Skeeter, thank you very much. |
|
|
|
Cortez Mos
Junior Member
USA
3 Posts |
Posted - 10/17/2007 : 23:21:20
|
im trying to solve
Cos (-10) cos 35 + sin (-10) sin 35 each number in degrees please help me out here! |
|
|
|
the_hill1962
Advanced Member
USA
1439 Posts |
|
| |
Topic |
|
Interactive Math Goodies Software
Topic Locked
