Physics · Electrostatic Potential

Which represents the quantities involved in calculating the potential due to a dipole, if \( r \gg a \), the term \( r_1^2 \approx r^2 - 2ar\cos\theta \) is obtained by using:

1. Binomial theorem for expansion
2. Pythagoras theorem directly
3. Cosine rule of geometry in triangle \( \text{Or}_1q \)
4. Superposition principle of electric field