割圆术（刘徽）求π

pi.js

function cx(lastM, r) { //求圆心到等边形的垂直距离
    return Math.sqrt(r-Math.pow(lastM/2, 2));
}

function cm(lastM, r) { //求等边形边长
    var x = cx(lastM, r); //圆心到等边形边的垂直距离
    return Math.sqrt(Math.pow(r-x, 2) + Math.pow(lastM/2, 2));
}

function pi(t) {
    var n = 6; //等边形的边数
    var m = 1; //等边形边长
    var r = 1; //圆半径
    var p = (n * m) / (r * 2); //pi π
    while(t-- > 0) {
        n *= 2;
        m = cm(m, r);
        p = (n * m) / (r * 2);
    }
    console.log("n:%s", n);
    console.log("p:%s", p);
    return p;
}