Question 879385
A picture is really necessary to see this plainly enough; but circles centered at A and C each have radius 2; and therefore, circle centered at B has radius 1.


Draw a triangle so that CA is 4, and AB and BC each is 3.  Now draw the circles for each of those points as centers.  You can reckon radius of each of A and C is 2.  This helps you see that AB contains a radius of circle A, just found as 2, but AB length was given as 3; so by difference, the other part of the way from A to B is 1.