Geometry

A line and a circle intersect at A and B as shown below. Find the distance between A and B.    
The circle is x^2 + y^2 = 1, and the line is y = x.    

This is an easy one, I don't even have to draw it. 

The circle is centered on the origin with a radius of 1. 

The line crosses through the origin and intersects the circle.  

The distance between A & B is the diameter of the circle.  =  2 units      

_.