Find Area of A Rectangle With Shortcut

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    Area Rectangle
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Discussion Overview

The discussion revolves around finding the area of a rectangle given its perimeter of 72 cm. Participants explore methods and formulas to simplify the calculation, seeking shortcuts or tricks to determine the area without extensive calculations.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants note that with a fixed perimeter, there are infinitely many rectangles, indicating that additional information about the rectangle is necessary to calculate the area.
  • One participant proposes using a variable for height and derives a formula for area based on that variable, suggesting that the area can be expressed as \( A = (36 - h)h \), where \( h \) is the height.
  • Another participant explains that the semi-perimeter is 36, which leads to the conclusion that the maximum area occurs when the rectangle is a square, yielding an upper bound of 324 cm².

Areas of Agreement / Disagreement

Participants generally agree that more information is needed to find a specific area from the given perimeter. However, there are differing views on the methods to express the area and the implications of the semi-perimeter in relation to the maximum area.

Contextual Notes

The discussion includes assumptions about the dimensions of the rectangle and the relationship between perimeter and area, which are not fully resolved. The derivation of the area formula relies on the choice of height as a variable, and the implications of the semi-perimeter are also discussed without reaching a consensus.

susanto3311
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hi all...

how do you find area of a rectangle, if its perimeter of a rectangle is = 72 cm?

i mean how to easy find it without hard work.

do you have a formula or just tricks similar like..

http://calculus-geometry.hubpages.com/hub/How-to-Find-the-Area-Perimeter-and-Diagonal-of-a-Rectangle

thanks in advance...

susanto
 
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For a given perimeter, there are an infinite number of rectangles that will have that perimeter. We need more information about the rectangle.
 
MarkFL said:
For a given perimeter, there are an infinite number of rectangles that will have that perimeter. We need more information about the rectangle.

if perimeter of a rectangle is = 72 cm, counting area of a rectangle =...

i need simple formula to calculate it.
possible?
 
Well, suppose we let the height $0<h<36$ be a free variable, then the base $b$ is $b=36-h$. Thus the area $A$ is:

$$A=bh=(36-h)h$$

Thus we find:

$$0<A\le324$$
 
The sum of the base and the height must be equal to the semi-perimeter, which is 36...half of 72. And the maximum area comes from the base and height being equal. So the upper bound is $18^2=324$.
 

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