What is the perameter of a rectangle whose length is 40 cm and its diagonal is of 40 cm.

Dear student,

There is some error, in the provided question, because from the given dimensions, the rectangle is not possible. This is because, if
length, $l=40cm$ and,
Diagonal, $d=40cm$ then by using Pythagoras theorem,
Breadth,  

$$\begin{gathered} b=\sqrt{l^2-d^2} \\ b=\sqrt{{40}^2-{40}^2} \\ b=0 \end{gathered}$$

Here, in rectangle, breadth cannot be zero.

Therefore, rectangle is not possible.

Regards,