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The ideas in this geometry lesson are taken from Math Mammoth Geometry 1 book.

Area of triangles
Free geometry lesson plan from HomeschoolMath.net

Note how a triangle is always exactly HALF of a parallelogram. Therefore the AREA of a triangle must be HALF OF THE AREA of the parallelogram.         In these pictures you see the altitude drawn to the triangle. Note how the same altitude would work for the parallelogram, too.   Can you figure out the area of these triangles using that information?

The area of a  triangle is half of the area of the parallelogram  that has two same sides as the triangle. The area of a parallelogram is BASE ALTITUDE. The area of a triangle is therefore half of that, or    BASE ALTITUDE 2 The horizontal line symbolizes division.

Examples:

Note that the base does NOT extend to the altitude. The area is    4 4 2 = 16 2 = 8		Turn your head to see this situation.   The area is    4 6 2 = 24 2 = 12		Here it is easiest to think the base being on the "top".   The area is    5 3 2 = 15 2 = 7 1/2

Example problem types

1.  Find out the area of the following triangles.

[Pictures available in the ebook]

3.  Remember?  This figure is called a ___________________. Calculate the area of it by finding the area of the two triangles and the rectangle into which it is divided.