Найти производные второго порядка z*yy; z*xy если z=(x3-8y5)4

[latex]z=(x^3+8y^5)^4\\\\z'_{x}=4(x^3+8y^5)^3\cdot 3x^2=12x^2(x^3+8y^5)^3\\\\z''_{xy}=12x^2\cdot 3\cdot (x^3+8y^5)^2\cdot 40y^4=1440x^2y^4(x^3+8y^5)^2\\\\z'_{y}=4(x^3+8y^5)^3\cdot 40y^4\\\\z''_{yy}=4\cdot 3(x^3+8y^5)^2\cdot 40y^4\cdot 40y^4+4(x^3+8y^5)^3\cdot 160y^3[/latex]