| A | B |
|---|
| acute angle | an angle with a measure less than 90 degrees |
| right angle | an angle with a measure of exactly 90 degrees |
| obtuse angle | an angle measuring between 90 and 180 degrees |
| straight angle | an angle with a measure of exactly 180 degrees |
| reflex angle | an angle measuring between 180 and 360 degrees |
| acute triangle | an triangle in which all three angles are less than 90 degrees |
| right triangle | a triangle in which one angle measures exactly 90 degrees |
| obtuse triangle | a triangle with one angle measuring more than 90 (but less than 180) degrees |
| equilateral triangle | a triangle in which all three sides the same length (and all three angles have the same measure) |
| isosceles triangle | a triangle in which two sides have the same length (and two angles have the same measure) |
| scalene triangle | a triangle in which all three sides have different lengths (and all three angles have different measures) |
| parallel lines | two lines that even when extended infinitely will never intersect |
| intersecting lines | a pair of lines that meet or cross, and have one single point in common |
| perpendicular lines | a pair of lines that meet to form a 90 degree angle (actually four 90 degree angles) |
| transversal | a line that crosses another pair of lines (usually a set of parallel lines that is being crossed) |
| alternate angles | angles on opposite sides of a transversal and on opposite sides of the parallel lines (diagonally opposite each other) - they must be equal |
| complementary angles | a pair of angles that add up to 90 degrees |
| supplementary angles | a pair of angles that add up to 180 degrees |
| opposite angles | angles on opposite sides of an intersection point - they must be equal |
| corresponding angles | angles on the same side of a transversal and on the same side relative to both parallel lines - they must be equal |
| congruent triangles | triangles that are exactly the same size and shape |
| SSS | side, side, side - if all three sides of a pair of triangles are the same, the two triangles must be congruent |
| SAS | side, angle, side - if two sides and the angle between them are the same on a pair of triangles, the triangles must be congruent |
| ASA | angle, side, angle - if two angles and the side between them are the same on a pair of triangles, the two triangles must be congruent |
| AAA | angle, angle, angle - if all three angles are the same on a pair of triangles, they must be similar |
| similar triangles | triangles that have the same shape, but not necessarily the same size |
| corresponding sides | in two similar triangles, the corresponding sides are the ones that fall between the same pairs of angles on each triangle |
| ratio of corresponding sides | must be equal for all pairs of sides on similar triangles - thus if we know the ratio of one pair, we know the ratio of all 3 pairs |
