## Elementary Geometry for College Students (7th Edition)

First, we use the Pythagroean theorem to find: $4^2 = 2^2 + (\frac{x^2}{2^2}) \\ x^2 = 48$ We use the formula for area: $A = \frac{\sqrt3}{4}\times x^2\\A = \frac{\sqrt3}{4}\times 48 \\A= 20.8$