To change a complex number from rectangular form (a + bi) to polar form, just follow these easy steps:

1. Identify the Parts: Look at your complex number. Here, (a) is the real part and (b) is the imaginary part.

   For example, if you have (3 + 4i), then (a = 3) and (b = 4).

2. Find the Magnitude: Calculate the magnitude (r) using this formula:

   $r = \sqrt{a^2 + b^2}$

   For our example: $r = \sqrt{3^2 + 4^2} = \sqrt{9 + 16} = \sqrt{25} = 5.$

3. Calculate the Angle: Now, find the angle (\theta) using:

   $\theta = \tan^{-1}\left(\frac{b}{a}\right)$

   For our example: $\theta = \tan^{-1}\left(\frac{4}{3}\right) \approx 0.93 \text{ radians (or } 53.13^\circ\text{)}.$

4. Write in Polar Form: Finally, show the complex number in polar form:

   $r(\cos \theta + i \sin \theta) \text{ or } re^{i\theta}.$

   So, (3 + 4i) can be written as:

   $5\left(\cos(0.93) + i \sin(0.93)\right) \text{ or } 5e^{i0.93}.$