Expand:
(i) 
(ii) 
(iii) 
(i) We know that,
(a – b)3 = a3 – b3 – 3ab (a – b)
Using this formula, we get
= (2x)3 – (2/x)3 – 3 × 2x × 2/x (2x – 2/x)
= 8x3 – 8/x3 – 12 (2x – 2/x)
= 
(ii) We know that,
(a – b)3 = a3 – b3 – 3ab (a – b)
Using this formula, we get
= (3a)3 – (1/4b)3 + 3 × 3a × 1/4b (3a + 1/4b)
= 27a3 + 1/64b3 + 9a/4b (3a + 1/4b)
= 
(iii) We know that,
(a – b)3 = a3 – b3 – 3ab (a – b)
Using this formula, we get
= (4/5x)3 – (2)3 - 3 × 4x/5 × 2 (3a + 1/4b)
= 64/125a3 – 8 - 24/5x (4/5x - 2)
= 
2