Let z_n = ix_n
Then the sequence satisfies x_{n+1} = \frac{x_n+1}{x_n-1} which is easy to see satisfies x_{n+2} = x_n
From this it is easy to see that z2007=z1 which can be easily computed
If the complex sequence of numbers z0, z1, z2........satisfy z_0=i+\frac{1}{137} and for n≥1 z_{n+1}=\frac{z_n+i}{z_n-i}
then find the value of z2007
Let z_n = ix_n
Then the sequence satisfies x_{n+1} = \frac{x_n+1}{x_n-1} which is easy to see satisfies x_{n+2} = x_n
From this it is easy to see that z2007=z1 which can be easily computed