It seems like you're asking about the formula for the equivalent of something, but I need a bit more context to give you a precise answer. Are you referring to:
- The **equivalent resistance** in a circuit (for series or parallel combinations)?
- The **equivalent capacitance** or **inductance** in an LC circuit?
- The **equivalent force** in mechanics?
- Some other equivalent value (like voltage, current, etc.)?
Let me know which one you're referring to, and I'll provide the correct formula!