triangle etoile drawing

function draw_triangle(a, b, c) {
    let alpha = Math.acos((a*a+b*b-c*c)/(2*a*b));
    let beta = Math.acos((a*a+c*c-b*b)/(2*a*c));
    let k=1, str="";
    str = "*<br>";
    while( k/Math.cos(alpha)<=b ){
        let n = Math.round(k*Math.tan(alpha));
        str+="*";
        for(let i=1;i<n;i++)
            str+="<span class='hide'>*</span>";
        str+="*<br>";
        k++;
    }
    while( (a-k)/Math.cos(beta)>0 ){
        let n = Math.round((a-k)*Math.tan(beta));
        str+="*";
        for(let i=1;i<n;i++)
            str+="<span class='hide'>*</span>";
        str+="*<br>";
        k++;
    }
    str += "*";
    return str;
}