Hi advancedfunctions2010,

These angles are special angles.

Use your rules for a 45-45-90 triangle and then use your

rules for a 30-60-90 triangle.

First,

Rationalizing the denominator, we get

This value is the hypotenuse of the 30-60-90 triangle,

so we have CB as the short leg and it's equal to one-half the hypotenuse...

And...AB is the long leg which is the short leg times the square root of 3.