- sinx + cosx = (căn2)sin4x
- tan3x = cot2x
- cosx.cos2x.cos4x.cos8x = 1\16 THANKS!!!!!!
a,[TEX]sinx + cosx = \sqrt{2}sin4x \leftrightarrow \ \sqrt{2}sin(x + \frac{\pi}{4}) = \sqrt{2}sin4x [/TEX]
[TEX]\leftrightarrow \ sin(x + \frac{\pi}{4}) = sin4x [/TEX]
b, [TEX]tan3x = cot2x \leftrightarrow \ tan3x = tan \frac{1}{2x} [/TEX]
c, [TEX]cosx.cos2x.cos4x.cos8x = \frac{1}{16} [/TEX]
[TEX]\leftrightarrow \ 16cosx.cos2x.cos4x.cos8x =1 [/TEX]
[TEX]\leftrightarrow \ \frac{16sinx.cosx.cos2x.cos4x.cos8x}{sinx} = 1[/TEX]
[TEX]\leftrightarrow \ \frac{8sin2x.cos2x.cos4x.cos8x}{sinx} = 1[/TEX]
[TEX] \leftrightarrow \ \frac{4sin4x.cos4x.cos8x}{sinx} = 1 [/TEX]
[TEX]\leftrightarrow \ \frac{2sin8x.cos8x}{sinx} = 1 [/TEX]
[TEX] \leftrightarrow \ \frac{sin16x}{sinx} = 1[/TEX]
[TEX]\leftrightarrow \ sin16x = sinx [/TEX]
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