b, x, y, c are consecutive terms of a G.P.
β΄ x = br, y = br^2 , c = br^3
A.M. between b and c is a
β΄ ((b+c)/2) = a β 2a = b+c
2abc = (b+c)bc
= b^2 c + bc^2
= b^2 (br^3 ) + b(br^3 )^2
= b^3 r^3 + b^3 r^6
= (br)^3 + (br^2 )^3
= x^3 + y^3
β΄ x^3 + y^3 = 2abc β
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