Length times width.
A shape on a piece of paper has a perimeter. A pair of numbers doesn't have a perimeter.
The area will decrease but the perimeter can increase, stay the same or decrease depending upon how the piece was cut off.
Square with perimeter of 80
You take the human in question and have him or her lie down on a bed, then you take a fairly long piece of string or twine and lay it next to that person as closely as you can, all along his or her perimeter, then snip it off so that it is the length of that perimeter. Then, you can straighten out the piece of string and measure it with a ruler or tape measure.
For marking a perimeter or edge of a piece of wood so you have a guideline to cut along.
"Perimeter" is the distance around something, often a piece of land, or a closed geometric figure drawn on paper. The square root of 8 is neither of those things. It's just a number. A number doesn't have a perimeter.
A piece of A4 paper measures 297 millimetres in length and 210 millimetres in width. This means a total perimeter of (297 + 210) x 2 = 1014 millimetres.
24 inches
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For a flat shape, the 'perimeter' is the length of the piece of string you'd need to wrap around it exactly one time, and the 'area' is the whole place inside it, that you'd cover with paint or grass.
Wrap the strip of paper around the plate or can and mark it where it completes a full circle around the object. Then lay the strip on a flat surface and measure the marked length using the ruler. That length is the perimeter (circumference) of the round object.
Only if you have one additional piece of information, such as that it is a rectangle or a triangle, or that all sides are equal.