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Simple trigo (Posted on 2014-01-03) Difficulty: 2 of 5
Find the value of

(i)cos 36
(ii)tan 15

using geometry.

No Solution Yet Submitted by Danish Ahmed Khan    
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Hints/Tips tan15 FIRST | Comment 1 of 6


1.       Draw a rectangle ABCD  s.t   AB=CD=1  ;AD=BC=2. 

2.       On the side CB mark a point  E  s.t.  AD=AE= 2 . 

3.       Now CE=2- sqrt(3)       angle BAC=60o. 

4.        So angle CDE=15o   (since angle AED=(150O- 30o)/2=75o). 

5.       Since tan 15o =CE/CD        tan 15o  =(2- sqrt(3))/1.  

6.       finally  tan 15o = 2- sqrt(3) 

7.       The above equals      approximately   .268

2nd part later (time allowing)

Edited on January 3, 2014, 2:48 pm
  Posted by Ady TZIDON on 2014-01-03 14:45:39

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