# geometry help

• April 3rd 2008, 01:36 PM
sri340
geometry help
In quadrilateral ABCD AB=5, BC =8, and CD = 20 units angle B and C both right angles . what is length of segment AD ?

answer was 17 units how ? my answer was different how ?

sri
• April 3rd 2008, 01:49 PM
Moo
Hello,

Let E (on [DC]) be the point such as ABCE is a rectangle.
Its dimensions are 8x20

So you have DE=DC-EC=20-5=15
AE=BC=8

ADE is a rectangle triangle in E, so you can use the Pythagorean theorem and have AD
• April 7th 2008, 02:34 PM
veronica mars
what did u get??
i thought i was doing it right, but i got 20.61552813
• April 7th 2008, 06:57 PM
Soroban
Hello, sri340!

Quote:

In quadrilateral $ABCD\!:\;\;AB=5,\;BC=8,\;CD = 20.$
$\angle B \,=\,\angle C \,=\,90^o$
What is length of segment $AD$ ?

. . But it looks like you played the ${\color{blue}J\heartsuit}$ instead of the ${\color{blue}3\clubsuit}$
```                  A  5  B                   * - - - *                 * :      |               *  :      |             *    :8      |8           *      :      |         *        :      |     D * - - - - - + - - - * C       :    15    E  5  :       : - - - - 20  - - - :```
In right triangle $AED$, use Pythagorus:
. . . $AD^2 \;=\;DE^2 + AE^2$