# Interactive video lesson plan for: Area of a Circle minus an inscribed Triangle

#### Activity overview:

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http://geometrycoach.com/Geometry-Lesson-Plans/?pa=MOOMOOMATH
In this video you will learn how to find the area of a circle minus an inscribed triangle.

In order to find this area you find the area of the circle and subtract this inscribed triangle.

Transcript

Number five
What is the approximate area of the shaded region of circle x?
I will teach you a strategy for on this one.
What we need to do is find the area of the whole shape.
In this case it is the area of the circle.
Next we will have to remove the area of the unshaded area which is a triangle.
If I turn the picture sideways you can see it is a triangle.
We will find the area of the circle, and subtract the area of the unshaded triangle.
I will draw the outer Shape which is the circle, and subtract out the triangle.
What is the area of a circle?
What is the area of the triangle?
1/2 Base times the height.
Now I just identify my variables and plug them in the formulas.
Lets now figure out the radius and diameter.
What is he radius of the circle?
We know the diameter is 14 so the radius is 7.
Pi times 7 squared.
I will subtract 1/2 the base of the triangle times height.
What is the base, 14 and the height is the radius.
We know our radius is 7.
We will take 1/2 14 times 7 and that is the area of the triangle.
1/2 times 14 times 7
49 pi x 1/2 (14)(7)
49pi-49
Is this one of our choices?
No because it is an approximate value.
Grab our calculator and type in 49 then second function and carrot key to get my pi -49.
Notice I can put it all in at one time.
I get 104.9
Now lets look at our choices and which is the best choice?
Letter D 105 meters squared because this is area.

-~-~~-~~~-~~-~-
-~-~~-~~~-~~-~-

Tagged under: circle,area circle,area circle inscribed triangle,area triangle,geometry,finding area circle,inscribed triangle,area circle shaded area

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