Question

prove that if a number is doubled then its cube is 8 times the cube of the given number

Answer 1

suppose number x is doubled
now
$(2x) {}^{3} = 2 {}^{3} x {}^{} = 8x {}^{3}$

Answer 2

Heya. dear 
let a number = a
it's cube will be a×a×a = a³

now atq 2a 
it's cube will be 
2a ×2a ×2a => 8a³ or (2a)³