Corbett Maths
Enlargements with Negative Scale Factor
How will a scale factor affect a figure—negatively? Using a grid, the narrator of an engaging video performs a dilation with a negative scale factor. The presenter compares a positive scale factor with a negative scale factor to explain...
Corbett Maths
Enlargements Using Ray Method
Figure out what to do when there is no grid to count. Using a ruler and a sharp pencil, the narrator shows how to perform a dilation when the figure is not on a grid. The ray method works by drawing a ray from the center of dilation...
Corbett Maths
Enlargements with Fractional Scale Factors
Enlargements make it bigger, right? A video shows viewers how to perform a basic dilation with a fractional scale factor. They learn how to use the scale factor to find the location of the transformed vertex by multiplying the horizontal...
Corbett Maths
Finding the Centre of Enlargement
Where did the transformation begin? Using a ruler, the narrator of a short presentation shows how to find the center of enlargement for transformed figures. Worksheets provide the class members an opportunity to practice the newly...
Corbett Maths
Enlargements
Count on the scale to enlarge a figure. The video shows how to create an enlargement given a scale factor and a center of enlargement. The presenter multiplies the vertical and horizontal distance by the scale factor to find the new...
CK-12 Foundation
Dilation: Lesson
Dilation—more than just an eye opener! A short video introduces the concept of dilating a figure given a center and a scale factor. Using prime notation, the installment of a larger geometry playlist shows how to label dilated images.
CK-12 Foundation
Dilation in the Coordinate Plane: Lesson
Multiply coordinates to either shrink or enlarge a figure. An informative segment of a geometry playlist introduces dilation on the coordinate plane. The dilations in the resource use the origin as the center of dilation, which makes...
Mathematics Assessment Project
Modeling Motion: Rolling Cups
Connect the size of a rolling cup to the size of circle it makes. Pupils view videos of cups of different sizes rolling in a circle. Using the videos and additional data, they attempt to determine a relationship between cup...
Khan Academy
Khan Academy: Geometry: Incenter and Incircles of a Triangle
Explains that the intersection of the three angle bisectors of a triangle form the incenter of the triangle. [7:58]
Khan Academy
Khan Academy: Geometry: Inradius Perimeter and Area
Proof that the area of a triangle is equal to half the inradius times the perimeter of the triangle, or the area is equal to the inradius times the semiperimeter. This video also appears in the Geometry: Circles strand. [7:29]
Khan Academy
Khan Academy: Geometry: Corresponding Angle Equivalence Implies Parallel Lines
Proof by contradiction that if two lines cut by a transversal create congruent corresponding angles then the lines are parallel. [5:18]
Khan Academy
Khan Academy: Geometry: Two Column Proof Showing Segments Are Perpendicular
In this video tutorial [11:06], the instructor shows how to construct a two-column proof using triangle congruence postulates to prove that two line segments are perpendicular.
Khan Academy
Khan Academy: Geometry: Ca Geometry: Triangles and Parallelograms
In this video lesson [11:14], the instructor demonstrates solutions to problems #21-25 of California Geometry released state test questions. Problems address understanding of the triangle inequality theorem, angle relationships with...
Khan Academy
Khan Academy: Geometry: Common Orthocenter and Centroid
Proves that if the orthocenter and centroid are the same point in a triangle then the triangle is a right triangle. [6:25]
Khan Academy
Khan Academy: Perpendicular Radius Bisects Chord
Proof that if a radius is perpendicular to a chord then it bisects the chord. This video also appears in the Geometry: Circles strand. [6:57]
Khan Academy
Khan Academy: Geometry: Similar Example Problems
Explains how to identify and use similar triangles in order to determine unknown side lengths in two given diagrams. Each diagram also applies knowledge of angles formed when parallel lines are cut by a transversal. [7:37]
Khan Academy
Khan Academy: Geometry:sss to Show a Radius Is Perpendicular to Chord It Bisects
Explains how to prove that a radius is perpendicular to a chord that it bisects by using the side-side-side triangle congruence postulate. [8:19]
Khan Academy
Khan Academy: Geometry: Euler Line
Demonstrates that the circumcenter, orthocenter, and centroid of a triangle all lie on a line called an Euler line. [6:12]
Khan Academy
Khan Academy: Geometry: Point Line Distance and Angle Bisectors
Proof that a point on the angle bisector is equidistant from each side of the angle and proof that a point that is equidistant from each side of the angle lies on the angle bisector. [10:57]
Khan Academy
Khan Academy: Geometry: Median Centroid Right Triangle Example
This video tutorial [9:00]explains how to find various measures of triangles formed by the medians of a right triangle. Based on the properties of the medians of a triangle, properties of centroids, and the Pythagorean theorem.
Khan Academy
Khan Academy: Geometry: Congruent Triangle Proof Example
Demonstrates how to use triangle congruency to prove that a given point is the midpoint of a given line segment. The proof is written in the form of a two-column proof. Practice problems available. [5:46]
Khan Academy
Khan Academy: Geometry: Circumcenter of a Right Triangle
Proves that the circumcenter of a right triangle is the midpoint of the hypotenuse. [5:42]
Khan Academy
Khan Academy: Geometry: Example Involving Isosceles Triangle and Parallel Lines
Demonstrates how to use the triangle sum theorem, properties of isosceles triangles, and special angle pairs formed when parallel lines are cut by a transversal to set up an equation using given algebraic expressions for angle measures...
Khan Academy
Khan Academy: Geometry: Ca Geometry: More Proofs
Demonstrates solutions to problems #7-10 of California Geometry released state test questions. Problems address understanding of congruent angle pairs when parallel lines are cut by a transversal, counterexamples, and properties of the...