lean_workbook_plus_50346

well, first of all i think its rearangment as well, but those can be done by am-gm in most cases:\n $\frac{a^3b+a^3c+ab^3+ac^3}{2}\ge2\cdot\sqrt[4]{a^8b^4c^4}=2a^2bc$\n\ndo that cyclic with $a,b,c$ and add them up u get the needed inequality