Answer:
1.25 cm
Explanation:
Draw a radius line from the center to one of the top corners. This forms a right triangle where the hypotenuse is r, the width is 1, and the height is 2−r. Using Pythagorean theorem:
(2−r)² + 1² = r²
4 − 4r + r² + 1 = r²
5 − 4r = 0
r = 5/4
r = 1.25