Copyright by The Goodheart-Willcox Co., Inc.
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Section 4 Measurement
Area of a Square
To calculate the area of a square, multiply the two sides.
A = 7″
×
7″
A = 49 in2
Area is always expressed in square units, such as square feet, square millimeters, square
miles, etc. Remember the rules for calculating denominate numbers. When two denominate
numbers are multiplied together, their units combine. When those two units are the same, they
become a squared unit, as seen in the example above. Review the principles of denominate
numbers in Units 1–5. Common notations for area include the following:
49 square feet
49 sq/ft
49 ft2
49 sq. ft.
750 mm2
Rectangle
A rectangle is a shape having four sides, with its opposite sides being parallel and equal
in length, and all its angles being 90°. It is similar to a square except one side is longer (length)
than the adjacent side (width).
Perimeter of a Rectangle
To calculate the perimeter of a rectangle, add the four sides.
P = 21.3″ + 21.3″
″
+ 9.5″
″
+ 9.5″
″
P = 61.6″
90° angle
Parallel sides
Length
Parallel
sides
Width