Method for finding radius of ellipse

Question

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I found a formula on the web but i have trouble translating it into a js function.
I tried to find the result without any lucky, see my code so far:

JavaScript

function getRadius(a, b, degrees) {
  var t = degrees * (Math.PI / 180); //radians
  var r = (a * b) / Math.sqrt((b * Math.cos(t))^2 + (a * Math.sin(t))^2);
  alert(r);
}

getRadius(560, 336, 45); // should give a result approx middle of 560 and 336

Can someone help me in building this method or just get the formula correct in JS?

Posted 16-Jul-13 11:48am

magnihan

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Comments

Yuriy Loginov 16-Jul-13 17:55pm

try using Math.pow(2) instead of x^2. check the javascript math API: http://www.w3schools.com/jsref/jsref_obj_math.asp

magnihan 16-Jul-13 18:03pm

I have not tested this yet, but now i got a 407 result thats indeed in the range i was looking for.

Edited line of code:
var r = (a * b) / Math.sqrt( Math.pow(b * Math.cos(t), 2) + Math.pow(a * Math.sin(t), 2) );

Yuriy Loginov 16-Jul-13 20:06pm

Another thing you may want to do is to convert your a and b parameters to floating point values. One way to do it is: a = a * 1.0

Sergey Alexandrovich Kryukov 16-Jul-13 20:13pm

What's wrong with just reading the JavaScript reference?
—SA

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