Samyak Jain
Last Activity: 5 Years ago
2(y – a) is HM between y – x and y – z.

y – x , 2(y – a) , y – z are in HP.
i.e. 1 / (y – x) , 1 / 2(y – a) , 1 / (y – z) are in AP.

2 . {1 / 2(y – a)} = 1 / (y – x) + 1 / (y – z)
1 / (y – a) = 1 / (y – x) + 1 / (y – z)

1 / (y – a) – 1 / (y – x) = 1 / (y – z)
(y – x – y + a) / (y – a)(y – x) = 1 / (y – z)
– (x – a) / (y – a)(y – x) = 1 / (y – z)

(x – a) / (y – x) = (y – a) / (z – y)
(x – a) / [(y – a) – (x – a)] = (y – a) / [(z – a) – (y – a)]
By invertendo, [(y – a) – (x – a)] / (x – a) = [(z – a) – (y – a)] / (y – a)
i.e. {(y – a) / (x – a)} – 1 = {(z – a) / (y – a)} – 1

(y – a) / (x – a) = (z – a) / (y – a)
(y – a)2 = (x – a)(z – a) i.e. (x – a) , (y – a) , (z – a) are in GP.