1) 2(1-cos²x)-3cosx-3=0
2-2cos²x-3cosx-3=0
-2cos²x-3cosx-1=0
2cos²x+3cosx+1=+
cosx=t , |t|≤1
2t²+3t+1=0
t=-1 или t=-1/2
cosx=-1 cosx=-1/2
x=π+2πn x=-π/2 +2πn
2) π≤π+2πn≤3π π≤-π/2+2πn≤3π
0≤2πn≤2π 3π/2≤2πn≤7π/2
0≤n≤1 3/4≤n≤7/4
n=1 n=1
x=π+2π×1=π+2π=3π x=-π/2+2π*1=3π/2
