It's not trigonometry. It is simple addition and subtraction.
Just measure from either the bottom or top mount holes to the bottom of the TV.
The contradictions are the same as in binomial probability
https://plainmath.net/secondary/statistics-and-probability/high-school-probability/binomial-probability when you need to find the answer to your question.
Now if you take the measurement from the lowest mounting hole of the TV, subtract that number from the distance of that lower mounting point on the stand to the base of the stand. That will tell you how much room you have for your center channel speaker.