How can I solve these trigonometric equations?

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SUMMARY

The discussion focuses on solving the trigonometric equation ab2cos(2x)(cos(x))2 + ba2sin(2x)(sin(x))2 = 0. Participants suggest transforming the equation into a more manageable form, specifically 2[tan(x)]3 - 2tan(x) = -b/a and tan(2x)(tan(x))2 = -b/a. The recommended approach involves expressing tan(2x) in terms of tan(x), substituting a variable for tan(x), and solving the cubic equation derived from the relationships established.

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kristo
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Homework Statement


The original problem is this: ab^2*cos(2x)*(cos(x))^2 + ba^2*sin(2x)*(sin(x))^2 = 0
And some of the more "logical" forms I've got to are these:2[tan(x)]^3-2tan(x) = -b/a
tan(2x)*(tan(x))^2=-b/a
But I can't solve these equations so I'd like to ask for some help here.
 
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Hi kristo! :smile:

(try using the X2 tag just above the Reply box :wink:)
kristo said:
tan(2x)*(tan(x))^2=-b/a

That's the one!

Now just write tan(2x) in terms of tanx, and solve. :wink:

(eugh … it's a cubic )
 
try to assign a variable like u to tanx
then establish a relation between tanx and tan2x
and then write both equations in terms of u and equate both to each other
and then solve the resultant equation for u
 

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