Geometry — Key Formulas & Concepts

Triangles:

Angles sum to 180. Area = 1/2 base x height.

Pythagorean theorem: a2 + b2 = c2

Special triangles: 30-60-90 (x, x sqrt 3, 2x) and 45-45-90 (x, x, x sqrt 2)

Circles:

Area = pi r2. Circumference = 2 pi r.

Arc length = (central angle / 360) x circumference

Quadrilaterals:

Rectangle area = length x width

Parallelogram area = base x height

Trapezoid area = 1/2 (base1 + base2) x height

Coordinate geometry:

Distance = sqrt((x2-x1)2 + (y2-y1)2)

Midpoint = ((x1+x2)/2, (y1+y2)/2)

Slope = (y2-y1)/(x2-x1)

GRE note: No proofs. No trig beyond SOH CAH TOA basics. Geometry is about 15% of quant.

Reference:

Wikipedia: Geometry

https://en.wikipedia.org/wiki/Geometry