Final answer:
The measure of AD in a rhombus when GD is given can be found using the Pythagorean theorem.
Step-by-step explanation:
If GLAD is a rhombus, the measure of AD can be found using the Pythagorean theorem. In a rhombus, all sides are equal.
Let's assume the length of AD is x. Since GD is given as 15 units, we can set up the equation x^2 = GD^2 + AD^2. Substituting the values, we get x^2 = 15^2 + x^2.
Simplifying this equation, we find that x = 15 units.