S-Cool Revision Summary

For a regular polygon with 'n' sides:

External angle = 360/n

For a regular polygon with 'n' sides:

Internal angle = 180 - 360/n

Polygon:	Number of sides:	External angles:	Internal angles:
Triangle	3	120	60
Square	4	90	90
Pentagon	5	72	108
Hexagon	6	60	120
Heptagon	7	51.4	128.6
Octagon	8	45	135
Nonagon	9	40	140
Decagon	10	36	144
Undecagon	11	32.7	147.3
Dodecagon	12	30	150

Special types of triangle

Sides:

Equilateral - All 3 sides equal and all 3 angles equal (to 60^o).

Isosceles - Two sides the same and the angles at the bottom of those sides are equal.

Scalene - No sides or angles equal.

Angles:

Acute-angled - All angles are acute (less than 90^o).

Right-angled - One angle is 90^o.

Obtuse-angled - One angle is obtuse (greater than 90^o).

Quadrilaterals:

Square - All sides equal, all angles 90^o, 4 lines of symmetry, rotation symmetry of order 4.

Rectangle - Two pais of equal and parallel sides, all angles 90^o, two lines of symmetry, rotation symmetry of order 2.

Rhombus - All sides equal, opposite sides parallel, two lines of symmetry, rotation symmetry of order 2. (Basically a square leaning over. Sometimes referred to as a diamond!

Parallelogram - Two pairs of equal and parallel sides, opposite angles equal, no lines of symmetry, rotation symmetry of order 2. (Basically a rectangle leaning over.).

Trapezium - One pair of parallel sides, no symmetry.

Kite - Two pairs of equal sides next to each other, one line of symmetry, no rotation symmetry, string (only joking!).

Circles

Circumference = 2πr

Or, if you want to use the diameter:

Circumference = πd

Area = πr²