Solution
= Solution
For real $\lambda$, the numerator and denominator have equal <complex modulus>:
$$
|\lambda-i|=\sqrt{\lambda^2+1}=|\lambda+i|.
$$
The denominator is always nonzero. Hence
$$
\boxed{|w|=\frac{|\lambda-i|}{|\lambda+i|}=1.}
$$
Thus the real axis maps into the unit <circle> in the <complex plane>.