Concept:
Two complex numbers having same argument lie on same ray from origin.
Step 1: Write polar forms.
\[
z_1 = r_1(\cos\theta + i\sin\theta)
\]
\[
z_2 = r_2(\cos\theta + i\sin\theta)
\]
Step 2: Relate them.
\[
z_2 = \frac{r_2}{r_1} z_1
\]
Let:
\[
k = \frac{r_2}{r_1} > 0
\]
\[
z_2 = kz_1
\]
\[
\boxed{z_2 = kz_1, \; k>0}
\]