How do I use the word "obtain" together with mathematical formulas?

Question

.What would be the correct version?

Answer 1

Don't use "that" with obtain. Instead, say "we obtain the result" x2+1=0, substituting your equation for the equation I used as an example. The London Mathematical Society has a guide here with more details: http://www.austms.org.au/Publ/Bulletin/writing.pdf