(x
2
−5x+2)(x
−5x−1)=28,
x
−5x=a,
(a+2)(a−1)=28,
a
+a−30=0,
1
=−6,a
=5;
−5x+6=0,
=2,x
=3;
−5x−5=0,
D=45,
3
=
5−3
5
,x
4
5+3
.