Question

Help please don't understand this question. Will medal!

Answer 1

a simple proof, can be this:

Here I consider a rectangle and its 2 diagonals

Answer 2

since a rectangle is a special parallelogram, then we can say that opposites sides are congruent. So we can write:
\[\begin{gathered}
AD \simeq BC \hfill \\
AB \simeq DC \hfill \\
\end{gathered} \]

Answer 3

Now I consider the subsequent triangles:

and

Answer 4

we can note that angles DAB and CBA are congruent since they are 90 degrees both

Answer 5

now, using the SAS criterion of similitude, I can say that the triangles ABC and ABD are congruent each other, in particular we can say that sides AC and BD are congruent each other