1
cosx=a
2a²-7a+3=0
D=49-24=25
a1=(7-5)/4=1/2⇒cosx=1/2⇒x=+-π/3+2πn,n∈z
a2=(7+5)/4=3⇒cosx=3>1 нет решения
2
8-8sin²x+6sinx-9=0
sinx=a
8a²-6a+1=0
D=36-32=4
a1=(6-2)/16=1/4⇒sinx=1/4⇒x=(-1)^n*arcsin1/4+πn,n∈z
a2=(6+2)/16=1/2⇒sinx=1/2⇒x=(-1)^n*π/6+πk,k∈z
3
tgx-4/tgx+3=0
tgx≠0⇒x≠πn.n∈z
tg²x+3tgx-4=0
tgx=a
a²+3a-4=0
a1+a2=-3 U a1*a2=-4
a1=-4⇒tgx=-4⇒x=-arctg4+πk,k∈z
a2=1⇒tgx=1⇒x=π/4+πm,m∈z