How to find nearest users from Latitude and Longitude

I want to need nearby users but I am getting this error

error : SQLSTATE[42000]: Syntax error or access violation: 1582 Incorrect parameter count in the call to native function 'radians' (SQL: select *, ( 6367 * acos( cos( radians() ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians() ) + sin( radians() ) * sin( radians( latitude ) ) ) ) AS distance from users having distance < 25 order by distance asc)

My Query :

 $user = User::where('id' , Auth()->user()->id)->first();
    $latitude = $user->lat;
    $longitude = $user->long;

    $suggestions = User::select(DB::raw('*, ( 6367 * acos( cos( radians('.$latitude.') ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians('.$longitude.') ) + sin( radians('.$latitude.') ) * sin( radians( latitude ) ) ) ) AS distance'))
                ->having('distance', '<', 25)
                ->orderBy('distance')
                ->get();

via Chebli Mohamed