Question 373619
This means the length of the side of an area, a rectangle for example, is always the same : 
 
 
If the side of the rectangle are a and b, then a+b times two is fixed, or, which is the same, the sum a and b is fixed.
 
A square of side 5, or a rectangle of side 4 and 6 have the same perimeter : 
 
4*5 for the square, 20, and 4+4+6+6=20 for the rectangle.
 
But the areas are 25 for square, and 24 for the rectangle.