theorem :: SERIES_3:28

for x, y, z being Real st x > 0 & y > 0 & z < 0 & (x + y) + z = 0 holds
(((x |^ 2) + (y |^ 2)) + (z |^ 2)) |^ 3 >= 6 * ((((x |^ 3) + (y |^ 3)) + (z |^ 3)) ^2)