cos4x - sin²(x) -1 = 0 hay sao á bạn !!!
b) [tex](sinx-cosx)^2 + 2sin^22x=1[/tex]
<=> [tex]sin^2x-2sinx.cosx+cos^2x + 2sin^22x=1[/tex]
<=> [tex]1-sin2x+2sin^22x=1[/tex]
<=>[tex]2sin^22x-sin2x=0[/tex]
=> sin2x = [tex]\frac{1}{2}[/tex] và sin2x=0
=> [tex]x= \frac{pi}{12}+kpi[/tex] ; x= [tex]\frac{5pi}{12}+kpi[/tex] ; x= kpi
c) [tex]sin^22x + cos2x=2sin2x[/tex]
<=> [tex]\frac{1-cos2x}{2}+cos2x= 1-cos2x[/tex]
<=> [tex]1-cos2x+4cos2x-1=0[/tex]
<=> [tex]3cos2x=0[/tex]
=> [tex]x= \frac{pi}{4}+\frac{kpi}{2}[/tex]