2sin²x-8sinxcosx+7cos²x-sin²x-cos²x=0
sin²a-8sinxcosx+6cos²x=0/cos²x≠0
tg²x-8tgx+6=0
tgx=a
a2-8a+6=0
D=64-24=40
a1=(8-2√10)/2=4-√10⇒tgx=4-√10⇒x=arctg(4-√10)+πn
a2=(8+2√10)/2=4+√10⇒tgx=4+√10⇒x=arctg(4+√10)+πn
2sin2xcos2x-cos²2x+sin²2x=0/cos²2x≠0
tg²2x+2tgx-1=0
tgx=a
a²+2a-1=0
D=4+4=8
a1=(-2-2√2)/2=-1-√2⇒tgx=-1-√2⇒x=-arctg(1+√2)+πn
a2=-1+√2⇒tgx=√2-1⇒x=arctg(√2-1)+πn
x=π-arctg(1+√2) U x=arctg(√2-1)