(x6/343) + (343/x6)
Above terms can be written as,
(x2/7)3 + (7/x2)3
We know that, a3 + b3 = (a + b) (a2 – ab + b2)
Where, a = (x2/7), b = (7/x2)
Then, (x2/7)3 + (7/x2)3 = [(x2/7) + (7/x2)] [(x2/7)2 – ((x2/7) × (7/x2)) + (7/x2)2]
= [(x2/7) + (7/x2)] [(x4/49) – 1 + (49/x4)]
(ii)8x3 – 1/27y3
Above terms can be written as,
(2x)3 – (1/3y)3
We know that, a3 – b3 = (a – b) (a2 + ab + b2)
Where, a = 2x, b = (1/3y)
Then, (2x)3 – (1/3y)3 = (2x – (1/3y)) ((2x)2 + (2x × (1/3y)) + (3y)2)
= (2x – (1/3y)) (4x2 + (2x/3y) + 9y2)
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