Подстановка условия
[src](-5*x^2)*y + 2*y^3 - x^4 + 5*x^4 + (5*x^2)*y + 8*y^3 при y = 1/3
(-5*x^2)*y + 2*y^3 - x^4 + 5*x^4 + (5*x^2)*y + 8*y^3
$$8 y^{3} + 5 x^{2} y + 5 x^{4} + - x^{4} + - 5 x^{2} y + 2 y^{3}$$
(-5*x^2)*(1/3) + 2*(1/3)^3 - x^4 + 5*x^4 + (5*x^2)*(1/3) + 8*(1/3)^3
$$8 (1/3)^{3} + (1/3) 5 x^{2} + 5 x^{4} + - x^{4} + 2 (1/3)^{3} + (1/3) \left(- 5 x^{2}\right)$$
(-5*x^2)/3 + 2*(1/3)^3 - x^4 + 5*x^4 + (5*x^2)/3 + 8*(1/3)^3
$$\frac{5 x^{2}}{3} + 5 x^{4} + - x^{4} + \frac{1}{3} \left(-1 \cdot 5 x^{2}\right) + \frac{2}{27} + \frac{8}{27}$$
$$4 x^{4} + \frac{10}{27}$$