289
(3y³-12y²-y+4)/(9y^4-1)=[3y²(y-4)-(y-4)]/(9y^4-1)=(y-4)(3y²-1)/(3y²-1)(3y²+1)=
=(y-4)/(3y²+1)
290
(x+5)/(x-1)+(2x-5)/(x-7)+(30-12x)/(x²-8x+7)=0
ОЗ x²-8x+7≠0
x1+x2=8 U x1*x2=7
x≠1 U x≠7
(x+5)(x-7)+(2x-5)(x-1)+(30-12x)=0
x²-7x+5x-35+2x²-2x-5x+5+30-12x=0
3x²-21x-5=0
D=441+60=501
x1=(21-√501)/6 U x2=(21+√501)/6