Khan Academy
Part 2 of Proof of Heron's Formula, Perimeter, Area, and Volume, Geometry
Picking up where the prior installment in the series on HeronÕs formula ended, Sal provides a more detailed explanation.
Corbett Maths
Coordinates and Shapes
Where is the point? Given three points on the coordinate plane, the video walks through the steps to find the location of the fourth point to create a given special quadrilateral. The narrator first determines the coordinates of the...
Brightstorm
Triangle Angle Sum
Don't believe everything that you hear — make them prove it! The video shows two methods to prove the Triangle Angle Sum Theorem. The following two videos apply the theorem to finding missing angle measures.
Flipped Math
Addition Postulate
Add a little algebra to the geometry. Class members learn about the Addition Postulate for segments and angles. The pupils use their knowledge of solving equations to find lengths of segments and measures of angles. Individuals apply...
Curated OER
What's a Venn Diagram, and How Do You Find the Intersection and Union of a Set?
A straightforward illustration of a Venn diagram. Intersection is what the sets have in common, and the union is all the elements of the sets. The diagram certainly helps you see what this means.
Khan Academy
Parallel Lines From Equation, Mathematics I, High School Math
Here is a fairly basic video that uses three equations, each written in slope-intercept form, to determine whether the lines are parallel. Sal graphs each equation on the same coordinate plane to show how their slopes compare. The video...
Khan Academy
Khan Academy: Geometry: Proof Sum of Measures of Angles in a Triangle Are 180
Proof that the sum of the angles in a triangle is 180 using the relationship of angles formed when parallel lines are cut by a transversal. This video also appears in the Geometry: Triangles strand. [6:31]
Khan Academy
Khan Academy: Geometry: Ca Geometry: Proof by Contradiction
Demonstrates solutions to problems #4-6 of California Geometry released state test questions. Problems address understanding of proof by contradiction and proving triangles congruent. [11:56]
Khan Academy
Khan Academy: Geometry: Proof Vertical Angles Are Equal
Proof that the measures of vertical angles are equal based on properties of supplementary angles. [4:51]
Khan Academy
Khan Academy: Worked Examples: Geometry: Ca Geometry: Proof by Contradiction
Students explore how to do a geometric proof by contradiction.
Khan Academy
Khan Academy: Geometry: Proof: Opposite Angles of Parallelogram Congruent
This video tutorial demonstrates how to prove that the opposite angles of a parallelogram are congruent based on knowledge of the special angles created when parallel lines are cut by a transversal. [4:08]
Khan Academy
Khan Academy: Geometry: Proof: Diagonals of Parallelogram Bisect Each Other
Demonstrates how to prove that the diagonals of a parallelogram bisect each other based on knowledge of the special angles created when parallel lines are cut by a transversal and the triangle congruency postulates. [9:06]
Khan Academy
Khan Academy: Geometry: Proof: Opposite Sides of Parallelogram Congruent
Demonstrates how to prove that the opposite sides of a parallelogram are congruent based on knowledge of the special angles created when parallel lines are cut by a transversal and the triangle congruency postulates. [8:30]
Khan Academy
Khan Academy: Geometry: Proof Rhombus Area Half Product of Diagonal Length
Demostrates how to prove that one way to find the area of a rhombus is by taking half the product of the diagonals. [5:07]
Khan Academy
Khan Academy: Geometry: Proof Rhombus Diagonals Are Perpendicular Bisectors
Demonstrates how to prove that the diagonals of a rhombus are perpendicular bisectors of each other based on knowledge of properties of parallelogram diagonals, triangle congruency, and supplementary angles. [4:04]
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...
Khan Academy
Khan Academy: Geometry: Equilateral Triangle Sides and Angles Congruent
In this video tutorial [6:29], the instructor models a proof so show that if the sides of an equilateral triangle are congruent, then all the angles are congruent and vice versa. The instructor uses the knowledge of congruent legs and...
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: 30 60 90 Triangle Side Ratios Proof
In this video tutorial [6:59], the instructor provides a proof for the relationship among the legs and hypotenuse of 30-60-90 triangles by breaking an equilateral triangle into two congruent triangles and using the Pythagorean threorem.
Khan Academy
Khan Academy: Geometry: Triangle Medians and Centroids (2 D Proof)
This video tutorial [15:15] provides a two-dimensional proof that the centroid is located two-thirds the way along every median of a triangle. This is a follow up to the proof in three-dimensions provided in the video, "Triangle Median...
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: Congruent Parts of Iscosceles Triangles
Proof that if the legs of an isosceles triangle are congruent then the base angles are congruent and vice versa using triangle congruency postulates. The proof is written as a two-column proof. [9:03]
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