我在做圆的时候出现拉一点问题 求大家帮我解答 着急

Question

function bb(){  var canvas = document.getElementById("canvas");  canvas.width = 260;  canvas.height = 260;  var context = canvas.getContext("2d");    context.beginPath()  context.lineWidth = 30  context.strokeStyle = "orange"  context.arc(130, 130,100,0,0.5*Math.PI)  context.stroke()  context.closePath()   context.beginPath()  context.lineWidth = 30  context.strokeStyle = "red"  context.arc(130, 130,100,0.5,1*Math.PI,false)  context.stroke()  context.closePath()   为什么我的第二段路径不从0.5PI起到1PI