Lines
Plane – A flat surface that has no thickness and extends
forever.
Point – an exact location
Line – a straight path that has no thickness and extends
forever in opposite directions
Ray – Part of a line that has one endpoint and extends
forever in one direction.
Line Segment – Part of a line that has two endpoints.
Congruent – figures that have the same shape or size.
(Same length for line segments).
Perpendicular lines – Two lines that make a 90 angle when
they intersect.
Parallel Lines – Lines that never intersect.
ANGLES
Right Angle – an angle that measures exactly 90o.
Acute Angle – An angle that measures greater than 0 o but less
than 90 degrees.
Obtuse Angle – An angle that measures greater than 90 o but
less than 180 o.
Straight Angle – Angle that measures exactly 1800.
Complementary angles – The sum of two angles equals 900.
Supplementary Angles – The sum of two angles equals 1800.
Adjacent angles – have a common vertex and a common side.
Vertical angles – opposite angles formed by two intersecting
lines.
Transversal – a line that intersects two or more lines.
Properties of Transversals to Parallel Lines
1. Corresponding angles are congruent
2. Alternate interior angles are congruent
3. Alternate external angles are congruent.
Polygons
Polygon – a closed plane figure formed by three or more line
segments.
Regular Polygon – a polygon in which all sides and all angles are
congruent.
Triangle – 3 sides, 3 angles
Quadrilateral – 4 sides, 4 angles
Pentagon – 5 sides, 5 angles
Hexagon – 6 sides, 6 angles
Heptagon – 7 sides, 7 angles
Octagon – 8 sides, 8 angles
Nonagon – 9 sides, 9 angles
Decagon – 10 sides, 10 angles
Triangles
Scalene triangle – no congruent sides.
Isosceles triangle – at least two congruent sides.
Equilateral triangle – all sides are congruent.
Acute triangle – all angles are acute
Obtuse triangle – has exactly one obtuse angle
Right Triangles
Right Triangle – has exactly one right angle.
Legs – two sides the form the right angle in a right triangle
Hypotenuse – The side opposite the right angle in a right
triangle. It is also the longest side.
The Pythagorean Theorem – A special relationship
between the sides of a right triangle.
a +b =c
2
2
2
Areas of Polygons
Area of a Triangle - A = 12 bh
Area of a Rectangle -
A = lw
Area of a Parallelogram - A = bh
Area of a Trapezoid - A = 12 h(b1 + b2 )
Quadrilaterals
Parallelogram – Opposite sides and opposite angles are congruent.
Rectangle – Parallelogram with four right angles
Rhombus – Parallelogram with four congruent sides.
Square – Parallelogram with four congruent sides and angles.
Trapezoid – A quadrilateral where exactly one pair of opposite
sides are parallel.
Polygon Measurements
The sum of the measures of a triangle is 180.
The sum of the measures of a quadrilateral is 360.
Perimeter
the distance around a geometric figure. To find the perimeter, add
the lengths of it’s sides.
Perimeter of a rectangle:
P = 2l + 2w
Circles
Circle – all points in a plane that are the same distance from a
given point, called the center of a circle.
Diameter – Line segment that passes through the center of a
circle and whose endpoints lie on the circle.
Radius – Line segment whose endpoints are the center of a
circle and any point on the circle.
Chord – Line segment whose endpoints are any two points on
a circle.
Arc – Part of a circle named by it’s endpoints.
Central Angle – An angle formed by two radii (radius).
Sector – part of the circle
enclosed by the two radii and
an arc connecting them.
Circumference of a circle.
Area of a Circle:
There are 3600 degrees in a circle.