google map Check the LatLng value is inside the Radius..?

Question

hi,

 

I need to find the the latitude langitude value is inside the Radius circle or not.if its is outside i have to pass some value from my MVC Controller.

 

i have tried this but data comes wrong distance, if the distance is acroos from the radius line i have to show some notification. if anybody knows this please help me for the same

function distance(lat1,lon1,lat2,lon2)
{
var R = 6371; // Earth's radius in Km
return Math.acos(Math.sin(lat1)*Math.sin(lat2) +
Math.cos(lat1)*Math.cos(lat2) *
Math.cos(lon2-lon1)) * R; }
if (distance(user.lat, user.lon, post.lat, post.lon) <= desiredRadiusInKm)
{ // return true;
} else
{ // return false;
}

i have tried this but data comes wrong distance,

 

if the distance is across from the radius line i have to show some notification. if anybody knows this please help me for the same

 

Thanks,