Ta có sinx+sin2x+sin3x=1⇔(sinx+sin3x)+sin2x=1⇔2sin2x.cosx+sin2x=1 ⇔2sin2x.cosx+1−2cos2x=1 $\Leftrightarrow 2\sin2x.\cos x -2\cos^{2}x=1$ den day ban giai tiep nhe
Ta có sinx+sin2x+sin3x=1⇔(sinx+sin3x)+sin2x=1⇔2sin2x.cosx+sin2x=1 ⇔2sin2x.cosx+1−2cos2x=1 $\Leftrightarrow 2\sin2x.\cos x -2\cos^{2}x=0$ den day ban giai tiep nhe