OpenSAT

Let's draw a diagram. The chord and the radii to the endpoints of the chord form an isosceles triangle, and the distance from the center of the circle to the chord is the altitude of this triangle. The altitude bisects the chord, creating two right triangles with legs of length 4 and a hypotenuse of length 5. Using the Pythagorean Theorem, we find that the altitude has a length of $\sqrt{5^2 - 4^2} = \sqrt{9} = 3$.