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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 11: sin2x +2cosx = 1 + sin4x – 4cosx Mọi người giải giúp mình vs ạ

Toán Lớp 11: sin2x +2cosx = 1 + sin4x – 4cosx
Mọi người giải giúp mình vs ạ

Comments ( 1 )

  1. sin2x +2cosx = 1 + sin4x – 4cosx
    ->2sinxcosx+2(2cos^2x-1)-1-sinx+4cosx=0
    ->sinx(2cosx-1)+4cos^2x+4cosx-3=0
    ->sinx(2cosx-1)+(2cosx-1)(2cosx+3)=0
    ->(2cosx-1)(2sinx+2cosx+3)=0
    ->\(\left[ \begin{array}{l}cosx=\frac{1}{2}\\2sinx+2cosx=-3\end{array}
     \right.\) 
    ->x=+-frac{pi}{3}+k2\pi
     

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222-9+11+12:2*14+14 = ? ( )