(x²-10x)²+8(x²-10x+25)-209=0
(x²-10x)²+8(x²-10x)+200-209=0
(x²-10x)²+8(x²-10x)-9=0
x²-10x=a
a²+8a-9=0
a1+a2=-8 U a1*a2=-9
a1=-9⇒x²-10x=-9
x²-10x+9=0
x1+x2=10 U x1*x2=9
x1=1 U x2=9
a2=1⇒x²-10x=1
x²-10x-1=0
D=100+4=104
x1=(10-2√26)/2=5-√26
x2=5+√26
Ответ x={1;9;5-√26;5+√26}