Constructors and Objects in java`

Constructors and Objects in java`

double x;
x =
69.2*(c1.(this.longitude)-c2.(this.longitude))*Math.cos((c1.(this.latitude)+c2.(this.latitude))/2);
what is wrong in this expression?
errors displa's as <identifier expected>
Here c1,c2 are the object of class City. This expression is in the
method(calculateDistance(City)) of a class City.. Plz Reply me