By definition, the area of a square is given by:
[tex] A = L ^ 2
[/tex]
Where,
L: length of the sides of the square.
Substituting values we have:
[tex] L ^ 2 = 81
[/tex]
From here, we clear the value of L.
We have then:
[tex] L = \sqrt{81}
L = 9 in
[/tex]
Answer:
the length of the cardboard is:
[tex] L = 9 in [/tex]
