Question 248317
http://www.sparknotes.com/math/geometry3/geometricproofs/section1.html
What do you know about rectangles?
Rectangles have four sides.
Opposite sides are equal
All angles are right angles
The diagonal makes a right triangle with the sides.
The right triangles are congruent then the diagonals must be congruent.
A triangle with sides L and W and a right angle between them has to be congruent with another right triangle with the same legs.