Square area with perimeter 10 equal to 6.25
where a is the side of the square.
where d is the diagonal of the square.
A square is a regular quadrilateral with all angles equal and all sides equal. Moreover, all the angles of the square are equal to 90°.
Square area formula 
where P is the perimeter of the square.
Solution:
S =
1
16
P2
=
1
16
102
=
6.25
Answer: the area of a square with a perimeter 10 equal to 6.25