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15*x^6-(((21*x^3)/3)*y^3) = 0
15*x^6-7*x^3*y^3 = 0
t_1 = x^3
15*t_1^2-7*t_1^1*y^3 = 0
15*t_1^2-7*t_1*y^3 = 0
DELTA = (-7*y^3)^2-(0*4*15)
DELTA = 49*y^6
49*y^6 = 0
49*y^6 = 0 // : 49
y^6 = 0
y = 0
DELTA = 0 <=> t_2 = 0
t_1 = (-(-7*y^3))/(2*15) i y = 0
t_1 = (7*y^3)/30 i y = 0
( t_1 = ((49*y^6)^(1/2)-(-7*y^3))/(2*15) or t_1 = (-(-7*y^3)-(49*y^6)^(1/2))/(2*15) ) i y > 0
( t_1 = (7*y^3)/15 or t_1 = 0 ) i y > 0
y+0 > 0
y > 0
y+0 > 0 // - 0
y > 0
t_1 = (7*y^3)/30
x^3-((7*y^3)/30) = 0
x^3+(-7/30)*y^3 = 0
1*x^3 = -(-7/30*y^3) // : 1
x^3 = 7/30*y^3
x^3 = 7/30*y^3 // ^ 1/3
x = (7/30)^(1/3)*y
t_1 = (7*y^3)/15
x^3-((7*y^3)/15) = 0
x^3+(-7/15)*y^3 = 0
1*x^3 = -(-7/15*y^3) // : 1
x^3 = 7/15*y^3
x^3 = 7/15*y^3 // ^ 1/3
x = (7/15)^(1/3)*y
t_1 = 0
x^3+0 = 0
x^3 = 0
1*x^3 = 0 // : 1
x^3 = 0
x = 0
x in { (7/30)^(1/3)*y, (7/15)^(1/3)*y, 0 }
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