2sin²x-8sinxcosx+7cos²x-sin²x-cos²x=0/cos²x
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,n∈z
a2=4+√10⇒tgx=4+√10⇒x=arctg(4+√10)+πn,n∈z
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