А) 5y^3-15y^2 -2y+6 = 0 y^2 -9 =0
5y^2(y -3) - 2(y - 3) = 0 (y-3)(y +3) =0
(y -3)(5y^2 -2) =0 y-3 = 0 y +3 = 0
y-3 = 0 5y^2 -2 = 0 y = 3 y = -3
y =3 5y^2 = 2
y^2 = 0.4
y = + - корень из 0,4
3y^3 -12y^2 -y +4 = 0 9y^4-1 = 0
3y^2(y -4) -(y -4) = 0 (3y^2 -1)(3y^2 +1) =0
(y-4)(3y^2 -1) = 0
y-4 = 0 3y^2 -1 = 0 3y^2 -1 = 0 3y^2 +1 =0
y = 4 3y^2 = 1 3y^2 = 1 3y^2 = -1
y^2 = 1/3 y^2 = 1/3 y^2 = - 1/3 не подходит
y= + - корень из 1/3