Question 393287
picture two radii of the circle
one drawn through the center of the chord
and the other, drawn to the end of the chord


the one through the center of the chord is a perpendicular bisector of the chord


a right triangle is formed by half the chord, 
the portion of the radius to the center of the chord (this is the distance from chord to center), 
and the radius to the end of the chord (this is the hypotenuse)


by Pythagoras ___ (5/2)^2 + x^2 = (9/2)^2