Subjects algebra

Cubic Curves

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Cubic Curves


1. Stating the problem: We are given two equations involving cubic terms: $$7x^3 - 3y^3 + 5xy - 2x - 27 = 0$$ and $$7x^3 - 7y^3 = 2(x - y)$$. 2. Simplify the second equation: $$7x^3 - 7y^3 = 2(x - y) \implies 7(x^3 - y^3) = 2(x - y)$$. 3. Factor the cubic difference in the second equation: $$x^3 - y^3 = (x - y)(x^2 + xy + y^2)$$, thus $$7(x - y)(x^2 + xy + y^2) = 2(x - y)$$. 4. If $x \neq y$, we can divide both sides by $(x - y)$: $$7(x^2 + xy + y^2) = 2$$, which describes a conic section. 5. Now consider the first equation: $$7x^3 - 3y^3 + 5xy - 2x - 27 = 0$$. It is a cubic curve with terms combining $x$ and $y$ in nonlinear ways. 6. To analyze both together, one can consider the system: $$\begin{cases} 7x^3 - 3y^3 + 5xy - 2x - 27 = 0 \\ 7(x^3 - y^3) = 2(x - y) \end{cases}$$. 7. Graphically, these represent two cubic curves intersecting symmetrically about the origin, creating intricate looping shapes. Final understanding: The curves describe implicit relationships in $x$ and $y$ with cubic terms, where the second equation simplifies to $7(x - y)(x^2 + xy + y^2) = 2(x - y)$, leading to the conic condition $7(x^2 + xy + y^2) = 2$ when $x \neq y$.