A rectangle's perimeter is the distance around it. To find the perimeter of a rectangle you must first know the measurement of its length and its width. The formula for perimeter is P = 2l + 2w (Perimeter equals two times the length plus two times the width). In some instances the length or the width will be a variable, or a letter representing an unknown number. You must first find the value of the variable before you can calculate the perimeter. For example: Find the perimeter of a figure that has a width of 4 feet and a length that is three times the width.
Instructions
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1
Multiply the width times 3 to get the length. 3 times 4 is 12. The length is 12.
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2
Write out the formula P = (2 x L) + (2 x W).
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3
Multiply the length times 2 and place the product into the formula. 12 times 2 is 24. The formula is now P = (24) + (2 x W).
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Multiply the width times 2 and place the product into the formula. 3 times 2 is 6. The formula is now P = (24) + (6).
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5
Add the products together to get the perimeter. 24 plus 6 equals 30.
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6
Include the unit of measure in your answer. The perimeter is 30 feet.