FlashMath | geometry

triangle properties

Sum of interior angles =
180°
Sum of exterior angles =
360°
Area =
½ × base × height
Pythagoras Theorem =
a² + b² = c²
Semi-perimeter (s) =
(a + b + c)/2
Heron’s formula =
√[s(s - a)(s - b)(s - c)]

circle properties

Circumference =
2πr
Area =
πr²
Diameter =
2r
Arc length (θ in radians) =
rθ
Sector area (θ in radians) =
½r²θ
Chord length =
2r sin(θ/2)

quadrilateral properties

Sum of interior angles =
360°
Area of square =
side²
Area of rectangle =
length × breadth
Area of parallelogram =
base × height
Area of rhombus =
(diagonal₁ × diagonal₂)/2
Area of trapezium =
½ × (sum of parallel sides) × height

polygon properties

Sum of interior angles =
(n - 2) × 180°
Sum of exterior angles =
360°
Number of diagonals =
n(n - 3)/2
Area of regular polygon =
(1/2) × Perimeter × Apothem

Measure of one interior angle (regular) =
[(n - 2) × 180°] / n
Measure of one exterior angle (regular) =
360° / n


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