>>605
>>612
y/x = v とおくと…
　log|x| = ∫(1/x)dx = ∫(1+v)/(1-2v-v^2)dv = (1/2)log(C) - (1/2)log| 1-2v-v^2 |,
　x^2 -2xy -y^2 = ±C,