So I have the following javascript code:

function dosine(){
    var num = document.getElementById('num').value;
    console.log(num);
    num = (num*Math.PI)/180;
    num = Math.sin(num);
    numinverse = Math.asin(num);
    num = num * (180/Math.PI);
    numinverse = numinverse * (180/Math.PI);
    document.getElementById('resultsine').innerHTML = "Sine: " + num.toString();
    document.getElementById('resultinverse').innerHTML = "Inverse Sine: " + numinverse.toString();
}

When I run this code and put in any number (in this case I used 64 for testing) the numinverse returns 64.00000000000001, I was just wondering why this is. I could obviously solve this by using toFixed, but I was wondering why this happened in the first place.