Shortcut Method to find out cubes of (99, 999 and 9999 etc.)

Shortcut Method to find out cubes of 
(99, 999 and 9999 etc.)

We know that (9)3 = 729 Now we can check how to find out the cube of 99.
To find out (99)3 take 729 as base and Insert a nine before 7 a zero before 2 and again a nine before 9 at last
i.e. 993 = 970299

To find out (999)3 insert two nines before 7, two zeros before 2 and two nines before 9 at last
i.e. 9993 = 997002999

To find out (9999)3 insert three nine before 7, three zeros before 2 and three nines before 9 at last 
i.e. (9999)3 = 999700029999 

∴ (99999)3 = 999970000299999