2
2сos²x-cosx-1=0
cosx=t
2t²-t-1=0
D=1+8=9
t1=(1-3)/4=-1/2⇒cosx=-1/2⇒x=+-2π/3+2πk,k∈z
t2=(1+3)/4=1⇒cosx=1⇒x=2πk,k∈z
0≤-2π/3+2πk≤3π/2
0≤-4+12k≤9
4/12≤k≤13/12
k=1 x=-2π/3+2π=4π/3
0≤2π/3+2πk≤3π/2
0≤4+12k≤9
-4/12≤k≤5/12
k=0 x=2π/3
0≤2πk≤3π/2
0≤4k≤3
0≤k≤3/4
k=0 x=0
3
делим на cos²x
2tg²x+4tgx-3=0
tgx=t
2t²+4t-3=0
D=16+24=40
t1=(-4-2√10)/4=-1-0,5√10
tgx=-1-0,5√10
x=-arctg(1+0,5√10)+πk,k∈z
t2=-1+0,5√10
tgx=-1+0,5√10
x=arctg(0,5√10-1)+πk,k∈z
x=π/2-arctg(1+0,5√10)
x=π+arctg(0,5√10-1)