Area of Triangles and Other Polygons

Recall that the area of a parallelogram is base x height.

If you divide a parallelogram into two congruent triangles, the area of each triangle is ½ x base x height.

Area of parallelogram = base x height;
cut the parallelogram in half on the diagonal
Area of a triangle = 1/2base x height

So the Area of a Triangle: A = ½ bh

In order to use the lengths of the legs of the triangle as the base and height, the legs must meet at a 90^o angle.

Watch the video below to learn more about finding the area of a triangle.

A trapezoid can be divided into a rectangle and two triangles. The area of a trapezoid is the sum of the areas of the rectangle and the triangles.

Area of a trapepezoid
Area = 1/2h(b1+b2)
Base1=top base
Base2=bottom base

Watch the video below to learn more about finding the area of a trapezoid.

L-shaped image on graph
The area is the number of 1X1 squares the shape covers. Count the numbers of squares covered.

You can find the area of irregular polygons by decomposing the polygon into rectangles, triangles and other shapes.

Here's the second page of the answer key.

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