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giải phương trình:
1) tg x+ cotg x = sin2x +cos 2x
2) cotg 2x = (cos^2 x - sin^2 x)/( sin^6 x +cos^6 x)
3) cosx.cos2x.cos4x.cos8x =1/16
4) tg x - sin2x -cos2x +2( 2cosx -1/cosx) =0
1) tg x+ cotg x = sin2x +cos 2x
2) cotg 2x = (cos^2 x - sin^2 x)/( sin^6 x +cos^6 x)
3) cosx.cos2x.cos4x.cos8x =1/16
4) tg x - sin2x -cos2x +2( 2cosx -1/cosx) =0