Term | Definition |
Isometry | Any rigid motion that preserves length or distance is an isometry. It can be shown that
under any isometry, the image of a line is a line, the image of a circle is a circle, and the images of parallel lines are parallel lines. |
Translation | A translation is a motion of a plane that moves every point of the plane a specified
distance in a specified direction along a straight line. |
Translation in a coordinate system | A translation is a function from the plane to the plane such that to every point (x,y) corresponds the point (x + a, y + b), where a
and b are real numbers. |
Rotation | A rotation is a transformation of the plane determined by holding one point, the center, fixed and rotating the plane about this point by a certain amount in a certain direction. |
Special rotation | A rotation of 360° about a point moves any point and hence any figure onto itself. Such a transformation is an identity transformation. Any point may be the center of such a rotation. A rotation of 180° about a point is a half-turn. |
Slopes of perpendicular lines | We can use transformations to investigate various mathematical relationships, including the slopes between two non-vertical perpendicular lines. If we rotate a line in the plane by 90 degrees about a point on the line, we have a perpendicular line. |
Reflection | A reflection in a line ℓ is a transformation of a plane that pairs each point P of the plane with a point P′ in such a way that ℓ is the perpendicular bisector of PP′, as long as P is not on ℓ. |
Glide reflection | Glide reflection, is a transformation consisting of a translation followed by a reflection in a line parallel to the slide arrow. |
Areas on a geoboard (dot paper) | Addition method divide an area into smaller pieces and then add the areas. |
Areas of a geoboard (dot paper) | Rectangle method is to construct a rectangle encompassing the entire figure and then subtract the areas of the unshaded regions. |
Pythagorean theorem | Given a right triangle with legs a and b and
hypotenuse c, c2 = a2 + b2. |
45 degrees 45 degrees 90 degrees right triangle | The length of the hypotenuse in a 45°-45°-90°
(isosceles) right triangle is the square root of 2 times the length of a leg. |
30 degrees 60 degrees 90 degrees right triangle | In a 30°-60°-90° right triangle, the length of the hypotenuse is twice the length of the leg opposite the 30° angle (the shorter leg). |