What is the formular for diagonals?

Answer 1

The diagonal of a rectangle can be found with the Pythagorean Theorem, since

the diagonal is the hypotenuse of the right triangle formed by the sides of the

figure. It is the square root of the sum of the squares of the two sides.

Finding the diagonal of a parallelogram would require some knowledge of trig.,

e.g. the law of cosines, or something equivalent.