Perimeter
is the distance around a figure. For a rectangle, we can find
perimeter using two methods:
- Using addition:
(l + l) + (w + w). Add the the length to its opposite side.
Add the width to its opposite. Find the sum of the lengths and
widths.
- Using multiplication:
(l x 2) + (w x 2). Multiply the length by 2. Multiply the width
by 2. Find the sum of the products.
Area is the amount
of square units inside a rectangle. Area is found by multipling
the length of the rectangle by the width:
We
use linear units when we measure perimeter.
Linear units measure one dimension, length. To show that
a rectangle has a perimeter of 24 inches, we would write
24 in.
We use square units
when we measure area. Square units measure two dimensions.
For instance, the area would be written 24 square inches.
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A
Mini-Movie Comparing Area and Perimeter
It's important to understand the
difference between perimeter and area, and to know that two shapes
may have the same perimeter, but different areas or may have the
same area, but different perimeters.
In the mini-movie below, you're
going to press the three buttons below the grid. With each press
the rectangle will change dimensions. Your job is to observe
what happens to the area and perimeter as the rectangle changes
dimensions.
Although
the area changes with each rectangle, the perimeter stays the
same. Do you think that it
is possible to have two rectangles with the same area but different
perimeters? Try the investigation below.
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Take
a piece of graph
paper and draw a rectangle with the dimensions 3 x 4.
Find the area and perimeter of the rectangle and then see
if you can draw another rectangle with the same area but
different perimeter. You can do the same with the following
areas:
32 sq. units
36 sq. units |
Everything
Geometry
The Basics| Classifying
Quadrilaterals | Classifying
Triangles
Area
& Perimeter | Angles
| Circles
