Giải phương trình lượng giác.

N

ngoc1thu2

giai pt luong giac

pt \Leftrightarrow sin2x + can3. cos2x +can3 =2( cos2x+ cos4x)
\Leftrightarrow1/2. sin2x+ can3/2 cos2x +can3/2 =cos2x+cos4x
\Leftrightarrowcos(2x-pi/6) +cos( pi/6) =cos2x +cos4x
\Leftrightarrowcosx.cos(x-pi/6) = cosx.cos3x
\Leftrightarrowcosx=0
hoac: cos( x-pi/6)= cos3x
den day ban tu giai tiep nhe (dung quen thank minh nua :D )
 
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