How to find the area of a triangle

Sunday, June 30, 2013
Finding the area of a triangle

In this video you will learn ….
How to find the area of a triangle
The formula for finding the area of a triangle
How to find the area of a right triangle
How to find the area of an acute triangle
How to find the area of an obtuse triangle

Transcript of the Video

Hi welcome to MooMooMath. Today we are going to talk about the area of a triangle. The area of a triangle is simple you just need to know a formula, and then just know the parts that fit into the formula so that you can solve it. So let’s look at the formula. The area of a triangle is one half the base times the height and that represents the area. So H is our height, but our height is really an altitude drawn from the peak down to the base which is the reference side of that altitude touches. There is another video on Heron’s formula if you don’t have the altitude. So here are three examples we have a right triangle, an acute triangle and an obtuse triangle, and it is three ways to look at it so bear with me as I go through each type. When you have a right triangle the one half times base times’ height is so simple. So let’s do that one first. We have a side of three and notice we have a right angle here. So that means that is the same as my altitude or my height. So three is my height so I will plug 3 in for my H. It touches the side that is the base of 4 so 4 is my base. So I will multiple 4 times 3 to get  12 and then half of 12 is 6 So three area of this triangle is 6 and that little double mark is inches so I put inches squared. Now let’s look at the acute triangle. All three angles are less than 90 so it is acute. We have an altitude drawn and the altitude is 8 and it touches this base which is 5 even if I had these two sides, if this side is nine (points to the side on the left) and this side is nine (touches side on the right) I still wouldn’t use those because I have an altitude or a height and the base already given. So I just multiple the base which 5 times the altitude which is 8 which is 40 and half of 40 is twenty so this one is 20 square inches. So that is how you handle an acute triangle. Last, let’s look at how we can handle the obtuse triangle. So know I have an obtuse triangle, I have two sides that are equal so I have 6 and this is 9 and outside the triangle I have the altitude drawn. So if I extend this out you can see the altitude is coming straight down here and is touching this base so whichever side it is touching I have to use that as my base. So 5 is my height or altitude and 5 would be my base and I would not use this side of 9 at all. So let’s plug in one half base times height  so one half 6 my base is 6 my height is 5, 5 times 6 is 30 and one half 30 is 15 so my area is 15. So this one would be 15 square inches. So those are the three cases. Hope this video was helpful.
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