[Toán 11] Phương trình lượng giác

B

buimaihuong

$\frac{1}{2}sin2x.(sin4x + sin2x) + \frac{1}{2}cos2x.(cos4x + cos2x) - 1=0$

$\frac{1}{2}sin2x.sin4x + \frac{1}{2}sin^{2}2x + \frac{1}{2}cos2x.cos4x + \frac{1}{2}cos^{2}2x - 1 = 0$

$\frac{1}{2}cos(4x - 2x) + \frac{1}{2}.(sin^{2}2x + cos^{2}2x) - 1 = 0$

$cos2x = 1$

$x = kpi$ $(k \in Z)$
 
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