1.

If H be the harmonic mean between x and y, then prove that \(\frac{H+x}{H-x}\) + \(\frac{H+y}{H-y}\) = 2.

Answer»

H being the H.M. between x and y

⇒ H = \(\frac{2xy}{x+y}\) ⇒ \(\frac{H}{x}\) = \(\frac{2y}{x+y}\) and \(\frac{H}{y}\) = \(\frac{2x}{x+y}\)

⇒ \(\frac{H+x}{H-x}\) = \(\frac{2y+x+y}{2y-(x+y)}\) and \(\frac{H+y}{H-y}\) = \(\frac{2x+x+y}{2x-(x+y)}\) 

(Using Componendo and Dividendo)

⇒ \(\frac{H+x}{H-x}\) = \(\frac{3y+x}{y-x}\) and \(\frac{H+y}{H-y}\) = \(\frac{3x+y}{x-y}\)

∴ \(\frac{H+x}{H-x}\) + \(\frac{H+y}{H-y}\) = \(\frac{3y+x}{y-x}\) + \(\frac{3x+y}{x-y}\) = \(\frac{3y+x-3x-y}{y-x}\) = \(\frac{2(y-x)}{y-x}\) = 2.



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