Question

giải phương trình sau : \(\cos^2x\cos2x=0\)

Answer 1

       cos²x.cos2x=0

<=>\(\left[\begin{array}{nghiempt}cos^2x=0\\cos2x=0\end{array}\right.\)<=>\(\left[\begin{array}{nghiempt}x=+-\frac{pi}{2}+kpi\\2x=\frac{pi}{2}+kpi\end{array}\right.\),

<=>\(\left[\begin{array}{nghiempt}x=+-\frac{pi}{2}+kpi\\x=\frac{pi}{4}+\frac{kpi}{2}\end{array}\right.\)