Draw in the red line and the two green lines: The red line is composed of two radii of length 1 each. Therefore the red line has length 2. The green lines are the equal length legs of an isosceles right triangle with red hypotenuse of length 2. Therefore the green lines each have length Each green line is made up of a radii of length 1, plus the radius of the small circle. Therefore the radius of the small circle is . Edwin