How to Prove Triangles are Similar
Students learn the following theorems related to similar
triangles. If an angle of one triangle is congruent to an angle of
another triangle, and the lengths of the sides that include each angle
are in proportion, then the triangles are similar (Side-Angle-Side
Similarity Theorem, or SAS Similarity Theorem). If the lengths of the
sides of two triangles are in proportion, then the triangles are
similar (Side-Side-Side Similarity Theorem, or SSS Similarity Theor

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How to Find the Perimeter of a Triangle
This is a very brief tutorial that focuses on solving the perimeter of a triangle. The teacher uses a small whiteboard for instruction. (01:51)
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Learn about Perimeter and Area - The video teaches students how to calculate the perimeter and area of figures. (05:36)
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[French For Kids] What Do They Do? Part 6
This brief video, which focuses on activities,Â has simple sentences spoken by a native speaker in French and the sentences are accompanied by appropriate images. The video, however,Â may be better served if the English translation were present, especially for beginning French learners. It is well-produced with clear sound.
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The History of Valentine's Day
This professional video explores the history and legends surrounding Valentine's Day. The presenter explains the legend of St. Valentine. The end of the video consists of impromptu interviews of customers at a greeting card store.  (03:59)
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Linear Inequalities - A Visual Proof
An instructor shows why we flip the sign when multiplying or dividing by a negative when solving inequalities. Â He uses a flip chart and shows several examples including both inequalities and word problems.
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How to Divide Inequalities
How to Divide Inequalities. Part of the series: Math FractionsÂ and Equations. When dividing inequalities, treat the equation like any other standard equation. Flip the inequality sign when dividing an inequality by a negative number with help from a math author and teacher.
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Graphing Linear Inequalities in Two Variables
This video begins with a simple inequality, then explains how to graph the inequality.Â  The instructor begins by showing how to graph the boundary line, then tells how to show the correct solution set on the graph by shading.Â

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Graphing Systems of Linear Inequalities
InÂ  this video, the instructor goes through the steps needed to graph a system of linear inequalities.Â  He discusses slope, shows how to draw the line on the coordinate plane, and explains what section of the graph should be shaded.Â  There is some shadow on the white board which makes it a little more difficult to see at times during the instruction.

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World War II: Invasion Of Poland - part 5/5
September 1939 - May 1940 The German and Soviet invasions of Poland, the Winter War, the sinking of the Graf Spee and Britain's apathy during the "phony war" until Britain's defeat in its first military engagement with German land forces in Norway, which led to the rise of Winston Churchill. Interviewees include Lord Boothby, Lord Butler, Admiral Charles Woodhouse, Sir Martin Lindsay and Sir John "Jock" Colville.
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Symptoms of Diabetes - Illumistream Health
One-third of diabetics donâ€™t know that they have the condition. This video can help you avoid being one of those undiagnosed. In this video, a doctor explains the risk factors, signs, and symptoms of diabetes.Â  2:55 min.
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Preventing Stroke
Up to 80 percent of strokes that occur in the United States each year could be prevented! In this video, a doctor give practical advice to stroke prevention.Â  3:33 min.
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Music Key Signatures Explained
This is an excellent teaching tool for high school and and advanced musical instumentalist.
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Scales octaves on a piano. This is a wonderful tool to use for instruction for middle and high school age children.
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Who Invented Subtraction?
Subtraction was invented in the same way as addition and
counting, in that it has always existed. In this video learn from a mathematics instructor who invented subtraction.

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When the Moors Ruled in Spain (4 of 11)
'The description Moors has referred to several historic and modern populations of Muslim (and earlier non-Muslim) people of Berber and Arab descent from North Africa, some of whom came to conquer and occupy the Iberian Peninsula for nearly 800 years' (Moors,Wikipedia, 2009). This video is suitable for older middle school and high school students.
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Dinosaur Builder
Step aside, bone diggers and fossil hunters. Scientists are now using computer modeling and a better understanding of living animals to bring dinosaurs back to life, virtually.
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Cold War: Soviet Dissolution - part 1/5
1989 - 1991 The U.S. proves the stronger, the Soviet Union implodes. Germany is reunified. Shorn of its empire and communist domination, Russia faces its future with its economy in chaos. The balance of terror that has kept the peace for more than 40 years vanishes. The Cold War has ended without the use of nuclear weapons.
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Cold War: Soviet Dissolution - part 2/5
1989 - 1991 The U.S. proves the stronger, the Soviet Union implodes. Germany is reunified. Shorn of its empire and communist domination, Russia faces its future with its economy in chaos. The balance of terror that has kept the peace for more than 40 years vanishes. The Cold War has ended without the use of nuclear weapons.
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D-Day to Berlin - The Battle for France (Part 4 of 6)
History Channel Video. 1944, Europe's future hung in the balance. Our 3-part series follows the story of Allied forces--from Normandy to the assault on Germany--and the victories that led to WWII's end in 1945. We begin on the day after D-Day, unfolding over the summer of 1944 as the initial narrow sliver of French coastline gained by the Allies is slowly extended. By the end of August, Allied victory seemed assured. Rommel had been wounded, Hitler was directing the battle, and the German army w
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