The right triangle CDE calculates DE=2.

The angle CED=60 degrees is calculated by Pythagorean theorem.

So calling AED is equal to 90 degrees.

AD= root number (DE square +AE square) = root number (4+3)= root number 7.

Take b as AE foot, and the square of AE is calculated as 3.

The answer is the root number 7.