It’s not like I was angry with her. Damn, I’d have to understand her for that to be a part of the equation.
What does the "that" stand for?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
That here refers to what was at issue in the previous statement, namely, "I was angry with her." So the character that makes this statement is saying:
I am not angry with her. If I was angry with her, I would have to understand her first. (= I need to understand her first to be mad at her. = I don't even understand her!)
You have stated that the part with the equation confuses you. Equation here doesn't mean a mathematical equation, but a situation. See this definition provided by the ODO:
(the equation): A situation in which several factors must be taken into account.
So you could say:
‘money also came into the equation’
which means money became part of the situation or problem
"other factors came into the equation"
means other factors have entered this situation to be considered.
So your original sentence
I’d have to understand her for that to be a part of the equation.
In order for that scenario (I am mad at her) to enter this situation, I would have to understand her to begin with.