The numbers will always be positive as these are squared numbers.
The numbers will always be negative numbers as it is the cube of negative numbers and the cube of negative numbers is always negative numbers.
and if x,y<0
if x,y<0 .
The sum of negative numbers is also negative . Therefore,
Now if a=x, b=y. Then,
Now combine the results of equation (1) and (2).
Hence, has been proved.