Question

To make a rectangular table more stable, a diagonal brace is attached to the underside of the table surface. If the table is 35 dm by 84 ​dm, how long is the​ brace?
The length of the brace is ___ dm.

Answer 1

If we draw a rectangle

                       35 dm
           -------------------------
           | -                            |
           |      -                       |
           |           -                  |  84 dm
           |                -             |
           |                    -         |
           |                        -     |
           |                            - |
            -------------------------

that diagonal (from one opposite corner to the other) forms two identical right traingles. the hypotenuse is the length of diagonal.
the legs are 35 dm and 84 dm.

by pythagorean theorem:

diagonal² = 35² + 84²
diagonal   = √(35² + 84²)
diagonal   = 91 dm

Answer 2

The answer would be 91 dm