Refer to the attached figure. We know that AB is 16 inches. We also know that AD=BD=10 and AE=BE=17
We're interested in DE, which we can compute as CD+CE
To compute CD, we can observe that ACD is a right triangle, and that AC is 8 inches long (it's half the base) and AD is 10 inches long (given).
So, by Pythagorean's theorem, we have
![CD = √(10^2-8^2) = √(36) = 6](https://img.qammunity.org/2020/formulas/mathematics/college/r29985qbqmyq8jjzphvz4ijtavr942brb1.png)
Similarly, we have
![CE = √(17^2-8^2) = √(225) = 15](https://img.qammunity.org/2020/formulas/mathematics/college/yvn8s0ci1nnt1cx3mgckuovyys6obq2x8h.png)
So, we have
![DE=CD+CE=6+15=21](https://img.qammunity.org/2020/formulas/mathematics/college/92vy7vhc10i3hnz68ug0z6n9286vo2tp14.png)