Citations in a math blog
Blog posts don't need to have a formal bibliography, but you should always provide attribution to others work, whether it is an original piece of research, or just a textbook whose presentation you are following. In a blog post, you can do this in a conversational style: point out results you enjoyed (with links!) and textbooks you find helpful. Not only will the folks you mention appreciate this, it will be helpful to your readers who want to follow up and learn more.