875
cos²x-3sinxcosx+sin²+cos²x=0/cos²x≠0
tg²x-3tgx+2=0
tgx=a
a²-3a+2=0
a1+a2=3 U a1*a2=2
a1=1⇒tgx=1⇒x=π/4+πn,n∈Z
a2=2⇒tgx=2⇒x=arctg2+πn,n∈z
877
1/2sin2x=-0,25
sin2x=-1/2
2x=(-1)^(n+1)*π/6+πn,n∈Z
x=(-1)^(n+1)*π/12+πn/2,n∈Z
878
√2(1/√2sinx+1/√2cosx)=√2
sinx*cosπ/4+sinπ/4cosx=1
sin(x+π/4)=1
x+π/4=π/2+2πn,n∈Z
x=π/4+2πn,n∈Z