Selective serotonin reuptake inhibitor. Selective serotonin reuptake inhibitors (SSRIs), also known as serotonin-specific reuptake inhibitors or serotonergic antidepressants,[1] are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder and anxiety disorders.
Then you're looking for the midpoint! The midpoint of a line segment is the point located midway between the endpoints of the line segment. This tutorial tells you about the midpoint of a line segment.
Here's the formula and I've got an example with numbers on the graph on the right: You don't really need to memorize the formula... Just remember that the midpoint is like the average point... So, you take the average of the x's and the average of the y's.