Question 1003087:  Use trigonometric identities to solve tan(2θ)+tan(θ)=0 exactly for 0≤θ≤π. 
 Answer by Alan3354(69443)      (Show Source): 
You can  put this solution on YOUR website! Use trigonometric identities to solve tan(2x)+tan(x)=0 exactly 
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tan(2x) = 2tan(x)/(1 - tan^2(x)) 
--> 2tan(x)/(1 - tan^2(x)) + tan(x) = 0 
tan(x) = 0 
--> x = 0, pi 
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2/(1 - tan^2(x)) + 1 = 0 
2/(1 - tan^2(x)) = -1 
(1 - tan^2(x))/2 = -1 
1 - tan^2(x) = -2 
tan^2(x) = 3 
x = sqrt(3) 
--> x = pi/3, 4pi/3 
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x = -sqrt(3) 
--> x = 2pi/3, 5pi/3 
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That's theta from 0 to 2pi.  If you only want up to pi eliminate the others. 
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