
Trigonometry Trigonometry Math Forum 
 LinkBack  Thread Tools  Display Modes 
June 3rd, 2015, 06:05 PM  #1 
Senior Member Joined: Jan 2015 From: USA Posts: 107 Thanks: 2  relationship between tangent, sine and cosine
Hi, how can I approach this problem? Also, could you tell me what results do you obtain?

June 3rd, 2015, 06:28 PM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,266 Thanks: 2434 Math Focus: Mainly analysis and algebra 
Find $\tan x$  perhaps you'll find it easier to write $t = \tan x$ and then solve for $t$. Once you have $\tan x$, you can picture a rightangled triangle to determine $\sin x$ and $\cos x$. My answers aren't pretty at all. Last edited by v8archie; June 3rd, 2015 at 06:33 PM. 
June 4th, 2015, 07:24 AM  #3  
Senior Member Joined: Jan 2015 From: USA Posts: 107 Thanks: 2  Quote:
Thanx! I got sinx= 2sqrt(39)/13 and cosx=sqrt(13)/13.  
June 4th, 2015, 09:17 AM  #4 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,780 Thanks: 1025 Math Focus: Elementary mathematics and beyond 
$\displaystyle \cos(x)=\frac{\sqrt3}{2},\sin(x)=\frac12$

June 4th, 2015, 10:14 AM  #5 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,780 Thanks: 1025 Math Focus: Elementary mathematics and beyond 
$\displaystyle \dfrac{1+\tan(x)}{1\tan(x)}=\tan(x+45^\circ)=2+\sqrt3$ $\displaystyle x+45^\circ=\tan^{1}(2+\sqrt3)$ $\displaystyle x=\tan^{1}(2+\sqrt3)45^\circ$ $\displaystyle \sin(x)=\sin(\tan^{1}(2+\sqrt3)45^\circ)$ $\displaystyle \sin(x)=\frac{\sqrt2}{2}\left(\dfrac{2+\sqrt3}{ \sqrt{8+4\sqrt3}}\dfrac{1}{\sqrt{8+4\sqrt3}}\right)=\frac{\sqrt2}{2 }\left(\frac{1+\sqrt3}{2\sqrt{2+\sqrt3}}\right)= \frac{\sqrt2}{2}\cdot\frac12\sqrt{\frac{4+2\sqrt3} {2+ \sqrt3}}=\frac{\sqrt2}{2}\cdot\frac{\sqrt2}{2}= \frac12$ $\displaystyle \Rightarrow\sin(x)=\frac12,\cos(x)=\frac{\sqrt3}{2 }$. Last edited by greg1313; June 4th, 2015 at 10:21 AM. 
June 4th, 2015, 12:43 PM  #6 
Global Moderator Joined: Dec 2006 Posts: 18,838 Thanks: 1564 
Note that tan(45° + 30°) = (1 + 1/√3)/(1  1/√3) = 2 + √3.

June 4th, 2015, 02:29 PM  #7 
Senior Member Joined: Apr 2014 From: Europa Posts: 571 Thanks: 176  Note $\displaystyle t = \tan x$ and solve for $\displaystyle t$ I got $\displaystyle t = \dfrac{\sqrt3}{3} \\\;\\ So,\ \ \tan x = \dfrac{\sqrt3}{3} \\\;\\ x=30^o \\\;\\ \sin 30^o = \dfrac{1}{2} \\\;\\ \cos 30^o = \dfrac{\sqrt3}{2} $ 

Tags 
cosine, relationship, sine, tangent 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Sine, Cosine, Tangent  matisolla  Trigonometry  8  February 28th, 2015 11:22 AM 
Cosine and Sine problem  iMath  Trigonometry  12  February 21st, 2012 12:22 AM 
Sine and cosine  johnny  Calculus  4  September 23rd, 2010 04:00 AM 
sine, cosine, etc  achmeineye  Trigonometry  6  March 12th, 2009 10:17 PM 
what does sine, cosine, tangent etc mean?  Vay  Trigonometry  3  January 25th, 2009 05:22 AM 