Update app.py

app.py

@@ -538,6 +538,7 @@ STRICT REQUIREMENTS:
    - When setting up differential equations either in calculus or differential equation applications
         * carefully consider the direction of change in variables
         * ensure integration bounds align with the physical direction of the process being modeled
+   - The solution must be analytical. It must not rely on numerical methods. 
 6. Maintain clear formatting
 7. At the end of the solution output, print SymPy code that you would use to solve or verify the main equations in the question 
 8. Observe the folloiwng SymPy Guidelines