I'm starting off my research paper with "Did you know that the framers of the Constitution were actually against political parties?"

Is it okay if after that I write, "That's right, they believed that political parties would corrupt the system."
Or is that too informal?

Far too informal...

Are you "starting off" your research paper, trying to figure out how to write the first paragraph? I certainly hope you have already done all these things before now!

1. Researched (read, taken notes, written down citation information for your Works Cited page).

2. Drafted your thesis statement (the main idea of your whole paper and your position about it)

3. Drawn up a detailed outline or plan to follow so you don't go "birdwalking" off-topic anywhere

4. Written at least a rough draft of the 2nd through next-to-last paragraphs.

5. Edited and proofed those paragraphs.

6. NOW you'd be ready to start drafting your introduction (which should end with your refined thesis statement).

7. Read through and edit your intro and internal paragraphs.

8. Draft your conclusion.

9. Edit and proof the entire paper.

10. Put your Works Cited together according to either MLA or APA guidelines, whichever your teacher has told you to use.

Here are some excellent websites to use, now and in the future:

https://www.powa.org/explain.html
Compete directions for planning and writing such a paper.

https://leo.stcloudstate.edu/acadwrite/thesistatement.html
How to tell if you have written an actual thesis statement.

https://leo.stcloudstate.edu/acadwrite/intro.html
Writing introductions

https://leo.stcloudstate.edu/acadwrite/conclude.html
Writing conclusions

https://owl.english.purdue.edu/owl/resource/747/01/
MLA guidelines for the paper and the Works Cited page.

https://owl.english.purdue.edu/owl/resource/560/01/
APA guidelines for the paper and the Reference List

In academic writing, it is generally recommended to maintain a more formal and objective tone. Including phrases like "That's right" might come across as too informal for a research paper. Instead, consider rephrasing it in a more neutral and scholarly manner. For example, you could write, "Indeed, the framers of the Constitution held the belief that political parties would have a corrupting influence on the system."

Remember, the goal of an academic research paper is to present a well-researched, logical, and objective analysis. By using a more formal tone, you can ensure that your paper maintains a sense of professionalism and credibility.