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2 * (-h3 + h2) / (h1 - h3) = 1/x + 1 - sqrt(1/x**2 + 1)
K - 1 - 1/x = - sqrt(1/x**2 + 1) K**2 - 2K - 2K/x + 1 + 2/x + 1/x**2 = 1/x**2 + 1 K**2 - 2K = (2K - 2)/x x = 2(K-1)/(K**2 - 2K)