X^3-y^3=98
xy^2-yx^2=-30
(x-y)(x^2+xy+y^2)=98
xy(y-x)=-30
xy(x-y)=30
x-y=30/xy
(30/xy)(x^2+xy+y^2)=98
30(x
^
2+xy+y
^
2)=98xy
30x
^2-68xy+30y
^
2=0 y<>0
30x
^
2/y
^
2 - 68xy/y
^
2+30=0
(x/y)=a
30a
^
2-68a+30=0
15a
^
2-34a+15=0
d=34
^
2-4*15*15=256=16
^
2
a1=5/3
a2=3/5
1) x/y=5/3
x=5y/3
(5y/3)
^
3-y
^
3=98
(125y
^
3-27y
^
3 )/27=98
98y
^3 /27=98
y
^3/27=1
y
^
3=27
y=3 => x=5
2) x/y=3/5
x=3y/5
(3y/5)
^3-y
^
3=98
27y
^
3/125 y
^3=98
(27y
^
3-125y
^
3)/125=98
-98y
^
3/125=98
-y
^
3/125=1
y
^
3=-125
y=-5 => x= -3