There are numerous formulas and equations that are important to memorize for the Electrical Engineering optional subject. These formulas and equations are crucial for understanding and solving various electrical engineering problems. Here are some of the key formulas and equations that should be memorized:

1. Ohm's Law:
- V = I * R
- Where V is voltage, I is current, and R is resistance

2. Power:
- P = V * I
- Where P is power, V is voltage, and I is current

3. Energy:
- E = P * t
- Where E is energy, P is power, and t is time

4. Kirchhoff's Laws:
- Kirchhoff's Current Law (KCL): The sum of currents entering and leaving a node is zero
- Kirchhoff's Voltage Law (KVL): The sum of voltages in a closed loop is zero

5. Capacitance:
- C = Q / V
- Where C is capacitance, Q is charge, and V is voltage

6. Inductance:
- L = Φ / I
- Where L is inductance, Φ is magnetic flux, and I is current

7. Transformers:
- V1 / V2 = N1 / N2
- Where V1 and V2 are voltages and N1 and N2 are the number of turns in the primary and secondary coils, respectively

8. Frequency:
- f = 1 / T
- Where f is frequency and T is period

9. Three-Phase Power:
- P = sqrt(3) * V * I * cos(θ)
- Where P is power, V is line voltage, I is line current, and θ is the phase angle

10. Fourier Series:
- f(t) = a0/2 + Σ[an*cos(nωt) + bn*sin(nωt)]
- Where f(t) is the periodic function, a0 is the DC component, an and bn are the Fourier coefficients, ω is the angular frequency, and n is the harmonic number

These are just a few examples of the important formulas and equations in electrical engineering. It is crucial to understand and memorize these formulas to effectively solve electrical engineering problems. Additionally, it is important to practice applying these formulas in various scenarios to gain a deeper understanding of their applications.