For reference, the post in question (keeping only English, with some small fixes to capitalization):
There are 3 vertices to define a triangle.
[1 2 3] [ 2 3 -2]
I am trying to compute the new vertices after rotate a triangle to have the left vertex move to a point y axis = -2, keep right vertex fixed. Which formula could be used to get the x axis of left vertex and (x,y) of top vertex of the new triangle?
The question you seem to be asking here is whether the last sentence clearly communicates what you want (the formula for the coordinates of the post-rotation vertices of the triangle). Yes, this sentence is an effective way to communicate this goal in English. The audience to which you are writing, however, does not speak exclusively English. If you wanted to improve this sentence, I would recommend doing it not with that language but simply by using mathematical notation. It is convention to name the points in a figure, like the vertices of your triangle, using letters. This convention is convenient here, as there is an established way to discuss points after a transformation; if you named the points on the initial triangle A, B, and C, starting from the left, your question could be more concise:
What formula would give the coordinates of A' and B'?
Using this point notation would also make the preceding passage more clear as well, as "left vertex" and "right vertex" are unusual terminology in a mathematical setting.
All that being said, the current English description does convey the right idea fairly well; the changes would just be to make it easier for your readers.
If you're communicating aloud, " B' " is pronounced 'B prime'