Question 448073
<pre><font face = "consolas" color = "indigo" size = 2><b>
{{{drawing(400,400,-6,6,-6,6,  circle(0,0,5),
line(-.41,.3,0,.65),line(0,.65,.3,.4), green(line(-4,3,3,4)),
line(-4,3,4,-3),locate(-4.3,3.5,B),locate(4,-3,C),line(0,0,3,4),
locate(3,4.5,A), locate(-.2,-.2,O),
locate(1.5,2,4)

  )}}}

Since OA is 4 and is a radius, and since OB is also a radius,
OB = 4 too. The Pythagorean theorem says

AB² = OA² + OB²
AB² = 4² + 4²
AB² = 16 + 16
AB² = 32
AB = <font face = "symbol">Ö</font>32 = <font face = "symbol">Ö</font>(16*2) = 4<font face = "symbol">Ö</font>2 or about 5.657 cm.

Edwin</pre>