The midpoint is the average of the x-coordinates and the average of the y-coordinates. From (2, 4) to (8, 10) the midpoint is (5, 7). Distance between the same points is a different formula, in the distance formula.
Add, then divide by two
((x₁ + x₂)/2, (y₁ + y₂)/2). If one coordinate is missing, set the average equal to the known midpoint and solve. A right-triangle check on the same segment is in the Pythagorean theorem.
Slope of that segment is in slope. The short list is in ACT Math formulas.
The bottom line
Midpoint: average the x's, average the y's.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.