1. Since you asked about step number 9 from your previous question, I need the context or the previous question to explain it properly. 2. Please provide the original problem or the previous steps so I can accurately explain step 9. 3. Without the original question or steps, I cannot determine what step 9 refers to. 4. Once you provide the previous question or steps, I will break down step 9 in detail with formulas and explanations.