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High school geometry
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Basics of geometry
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Geometric definitions
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Linear pair theorem
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Area of a regular polygon
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Diagonal length of a right rectangular prism
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Distance and midpoint in 3D
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Circumcircles and incircles
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Transformations
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Preserved properties of rigid transformations
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Find measures using rigid transformations
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Find the angle of rotation
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Find the sequence of rigid transformations
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Reflecting figures
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Reflecting a point over any non-horizontal line
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Congruence
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Congruent polygons
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Congruent supplements and complements theorems
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ASA and AAS congruence
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Isosceles triangle theorem and its converse
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SSS congruence
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SAS congruence
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Converse of the Pythagorean theorem
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Proving isosceles trapezoids
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Similarity
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Intro to similarity
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All circles are similar
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Finding angles and side lengths in similar polygons
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Finding the scale factor for similar polygons
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Third angle theorem
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Similar triangles
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Ratios of area, surface area, and volume, for similar shapes
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Crossed ladders theorem
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Polygons
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Perimeter of composite figures
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Finding the volume and surface area of composite figures
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Sum of the interior angles of a triangle
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Sum of interior angles for simple polygons
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Sum of exterior angles
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Incenter and circumcenter of a triangle
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Intro to the incenter and circumcenter of a triangle
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Perpendicular bisector theorem and its converse
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Circumcenter theorem
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Angle bisector theorem
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Incenter theorem
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Triangles
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Euler line
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Geometric mean theorem
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Triangle angle bisector theorem
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Ceva's theorem
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Proving the altitude of an isosceles triangle cuts two congruent right triangles
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Centroid and orthocenter
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Ordering triangle sides and angles
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Midsegment and proportionality theorems
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Menelaus's theorem
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Side splitter theorem
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Hinge theorem and its converse
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Hypotenuse-leg congruence theorem
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Areas of triangles and quadrilaterals on grids
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Exterior angle theorem
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Quadrilaterals
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Diagonals of a kite are perpendicular
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Diagonals of a parallelogram bisect each other
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Diagonals of a rhombus are perpendicular bisectors
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Area of a rhombus from diagonals
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Diagonals of a rectangle are congruent
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Opposite sides of a parallelogram are congruent
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Proving that opposite angles of a parallelogram are congruent
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British flag theorem
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Cyclic quadrilaterals
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Classifying quadrilaterals from four points
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Circle theorems
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Thales's theorem and its converse
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Central angle theorem
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Angles standing on the same arc are congruent
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Chord properties
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Congruent tangents theorem
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Radius and tangent theorem
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Radii inside right triangles
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Alternate segments theorem
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Power of a point
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Three squares puzzle
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Volume and surface area
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Cavalieri's principle
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Volume of prisms and cylinders
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Volume and surface area of a sphere
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High school geometry
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Polygons
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Sum of interior angles for simple polygons
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Other resources
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Sum of the interior angles for simple polygons
Proof: Sum of the interior angles of a simple polygon
YouTube videos
1300
Angle Sums of a Polygon (1 of 2: Interior angles)
Eddie Woo
15996
What is the interior angle sum theorem for polygons
Brian McLogan
14986
How to use triangles to find the measure of interior angles of a polygon
Brian McLogan