Until now, I thought that one can use the word "obtain" together with "that", as in
By ... we obtain that a²+b²=c².
(Many mathematicians who like me are not native speakers are doing this!) Now I found two documents saying that "that" doesn't belong here: This Polish site, and the guide of the London Mathematical Society to writing mathematics, which says that "obtain" should usually not be followed by "that".
Now my question: if instead of the above I write
By ... we obtain a²+b²=c².
how do I read that sentence? "We obtain a square plus b square equals c square"? Then it appears that I use "obtain" with the verb "equals", which sounds a bit strange to me.
What would be the correct version?