What is an Isosceles Triangle?

Tuesday, July 2, 2013
Isosceles Triangle
In this video you will learn
  • What an isosceles tiangle is.
  •  Definition for a isosceles triangle 
  •  that two of the  sides are congruent 
  •  that two sides are congruent Transcript
Isosceles Triangles
Hi welcome to MooMooMath. Today we are going to look at an isosceles triangle is and what are some of the properties. This is a really interesting triangle. An isosceles triangle is one that has two congruent sides. So in these two diagrams we have these two sides that are marked congruent or you can have two sides marked 5, 5 and 4 and then you can say. OK that’s an isosceles triangle because two out of the three sides are congruent.  The other way to look at it is with the perspective of the angles. We see this angle is 45 and this angle is 45 and this angle is 90 since we have two angles that are congruent it is an isosceles triangle. That would mean if I go to the opposite side this side (marks triangle) and this side (marks triangle) are the two congruent sides. In this case are the congruent legs because they are in a right triangle. OK let’s look at the rules of an isosceles triangle. An isosceles triangle is a triangle that has two sides that are congruent. (Which means equal length) or two angles that are congruent or have equal measure. So it can look like this. Let’s go back to this triangle one more time and get one more quick tip. This side is 5 let me give you an actual measure at the top. Let’s say we know the angle up here is forty degrees. Can we figure these other two angles? We can because we know the angles add to 180 degrees. If I have used up 40 degrees so you have 140 degrees left. Also I have these two base angles are congruent to each other so I can just take the 140 and divide by two and that gives me an angle measure of 70. So each of these base angles measure 70 degrees. So there is a helpful hint with isosceles triangles. Hope this was helpful.
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