[toán11]phương trình lượng giác

L

l94

[tex]cos^2x+2cos^22x+2cos^23x-3=cos^4x(2sin2x+1)[/tex]
[tex] \Leftrightarrow cos2x+cos4x+cos6x=cos^4x(2sin2x+1)[/tex]
[tex] \Leftrightarrow cos4x(2cos2x+1)=cos^4x(2sin2x+1)[/tex]
[tex] \Leftrightarrow (1-2sin2x)(1+2sin2x)(2cos2x+1)=cos^4x(2sin2x+1)[/tex]
[tex] \Leftrightarrow 2sin2x+1=0[/tex]
và [tex] (1-2sin2x)(2cos2x+1)=cos^4x[/tex]
......................
 
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