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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.ProblemFind all solution for the following equation on the interval 0x2: 5cos(x+3)=1.Solution5cos(x+3)=1cos(x+3)=1/5x+3=arccos(1/5)=1.369x=1.369-3=-1.125The 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 4.653Thank you for any help you can give me.

tkhunny

USA
1001 Posts

 Posted - 10/05/2007 :  21:49:25 1.369 - 3 = -1.631 NOT -1.125-1.631 + 2 = 4.653You 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

159 Posts

 Posted - 10/06/2007 :  00:03:52 quote:Originally posted by tkhunny1.369 - 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

USA
5634 Posts

 Posted - 10/06/2007 :  09:01:03 arccos(1/5) = 1.369, a quad I angle.x = 1.3694 - 3 = -1.631arccos(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

USA
1469 Posts

 Posted - 10/18/2007 :  06:34:57 This new problem was previously posted athttp://www.mathgoodies.com/forums/topic.asp?TOPIC_ID=32967quote:Originally posted by Cortez Mosim trying to solve Cos (-10) cos 35 + sin (-10) sin 35 each number in degrees please help me out here!
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