1. The user asked about the meaning of the letter "r" and "i". 2. In mathematics, "r" often represents a variable such as radius in geometry or a real number in algebra. 3. The letter "i" commonly represents the imaginary unit in complex numbers, defined as $$i^2 = -1$$. 4. "r" can also be used in various contexts depending on the problem, such as distance, rate, or radius. 5. "i" is fundamental in complex number theory and is used to express numbers that cannot be represented on the real number line. 6. If you have a specific context or equation involving "r" or "i", please provide it for a more detailed explanation.