Sinx=cos2x
sinx-1+2sin²x=0
sinx=a
2a²+a-1=0
D=1+8=9
a1=(-1-3)/4=-1⇒sinx=-1⇒x=-π/25+2πn,n∈z
a2=(-1+3)/4=1/2⇒sinx=1/2⇒x=(-1)^n*π/6+πk,k∈z
Sinx+sin3x=o
2sin2xcosx=0
sin2x=0⇒2x=πn⇒x=πn/2,n∈z
cosx=0⇒x=π/2+πk,k∈z
Sin²x-2sin2x-5cos²x=0
sin²x-4sinxcosx-5cos²x=0/cos²x
tg²x-4tgx-5=0
tgx=a
a²-4a-5=0
a1=a2=4 U a1*a2=-5
a1=-1⇒tgx=-1⇒x=-π/4+πn,n∈z
a2=5⇒tgx=5⇒x=arctg5+πk,k∈z