Jazakallah khair sir ! i understood! actually i did post this question again cuz my last post deleted by itself so i had to post it again …anyways thank you! 🙂 …plz also reply to my questions about wave equation …i can’t see that post on forum but whatever u post on forum about a certain topic it comes under every video of that topic ….so when i click on the post about WAVE EQUATION under the video then only it takes me to that post other wise i can’t find it like that