Radius to a Tangent

						var board = JXG.JSXGraph.initBoard('box1', {
boundingbox: [-10, 10, 10, -10],showNavigation:false, showcopyright: false, axis: false,
});

var p1 = board.create('point', [0, 2.0],{name:'O',face:'',label:{offset:[-20,0]}});
var c1 = board.create('circle', [p1, 6],);
var g1 = board.create('glider', [2.0, 1.5, c1],{name:'',face:''});
var t1 = board.create('tangent', [g1]);
var perp1 = board.create('perpendicularsegment', [t1, p1],{color:'blue'});
var g2 = board.create('glider', [6.0, 7.5, t1],{name:'',face:''});

var a1 = board.create('angle', [g2, g1, p1],{name:' ',radius:1.5});