Mathematics · Grades 6–8
Coordinate geometry · Formula sheet
Rules, conditions and small examples in one printable reference.
Remember this
Slope between two points
Keep the point order the same in numerator and denominator.
m = (y₂ − y₁)/(x₂ − x₁), x₂ ≠ x₁
(-51 − (4))/(21 − (10)) = -5
Midpoint coordinates
Average the x-coordinates separately from the y-coordinates.
M = ((x₁ + x₂)/2, (y₁ + y₂)/2)
(19 + (-12))/2 = 3.5
Reflection in a vertical line
The image is the same distance on the opposite side of the mirror line.
x′ = 2h − x; reflection in x = h
2 × (-2) − (9) = -13
Quarter-turn rotations
This rule rotates around the origin in the coordinate plane.
90° counterclockwise: (x,y) → (−y,x)
(-12, -21) → (21, -12)
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.