Normal
\[sin5x-sinx=4sinx\]\[->2sin3xcos2x=4sinx\]\[->(sin2xcosx+cos2xsinx)cos2x=2sinx\]\[->(2sinxcos^2x+cos2xsinx)cos2x-2sinx=0\]\[->sinx(2cos^2xcos2x+cos^2 2x-2)=0\]->thế là xong
\[sin5x-sinx=4sinx\]
\[->2sin3xcos2x=4sinx\]
\[->(sin2xcosx+cos2xsinx)cos2x=2sinx\]
\[->(2sinxcos^2x+cos2xsinx)cos2x-2sinx=0\]
\[->sinx(2cos^2xcos2x+cos^2 2x-2)=0\]
->thế là xong
