Geometry Cheat Sheet

Geometry Symbols

∠, ∠s Angle, angles
∠AB Measure of angle AB

Arc AB

Measure of arc AB
  Circle, circles

Congruent

Not congruent
° Degree
= Equal
Not equal
> Greater than
< Less than
AB Length of line segment AB
AB Line AB

Line segment AB

Ray AB
||
Parallel

Not parallel

Parallelogram
Perpendicular
˜ Similar
δ Triangle
(x, y) Ordered pair in plane
ab = cd Proportion
a: b or ab Ratio

Useful Abbreviations

AA Angle-angle, for proving triangles similar
AAS Angle-angle-side, for proving triangles congruent
ASA Angle-side-angle, for proving triangles congruent
cos Cosine
cot Cotangent
CPCTC Congruent parts of congruent triangles are congruent
csc Cosecant
CSSTP Corresponding sides of similar triangles are proportional
SAS Side-angle-side, for proving triangles congruent
sin Sine
tan Tangent

Common Variables

a Apothem
a, b, c Lengths of the sides of a triangle
A Area of a polygon
B Area of the base of a solid
C Circumference of a circle
h Height of an altitude
α Alpha (name of an angle)
β Beta (name of an angle)
Xx Unknown value
θ Theta (name of an angle)
π Pi
  Slant length of a side of a solid
l or l Length of a rectangle
L Lateral area of a solid
m Slope of a line
M Midpoint of a line segment
n Number of sides of a polygon
P Perimeter of a polygon
P or P' Plane
r Radius
s Length of the side of an equilateral polygon
S Surface area of a solid
T Total area
V Volume
w or w Width of a rectangle

Formulas You Should Know

Area (A) of a triangle A = ½bh where b measures the base and h the altitude
Perimeter (P) of a triangle P = a + b + c where a, b, and c are the lengths of the sides
Area (A) of a rectangle A = lw where l measures the length and w the width
Perimeter (P) of a rectangle P = 2b + 2h where b measures the width and h the height
Area (A) of a circle A = πr2 where r measures the radius
Area Circumference (C) of a circle C = 2πr or C = πd where r measures the radius and d the diameter