People around the world share knowledge to help others learn. However, while well intentioned, they may not be experts or know that exact situation or problem you face.
When searching the internet for math help, ask yourself:
Who is it written by and what are their credentials? (Authority)
When was it written and what context? (Currency and Purpose)
Is the author(s) work reliable and using known and standardized methods? (Reliablity)
Samuel C. Williams Library