Este contenido no está disponible en español
Accessing this course requires a login, please enter your credentials below!
Please confirm you want to block this member.
You will no longer be able to:
Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.
the point at which rays or waves meet after reflection or refraction, or the point from which diverging rays or waves appear to proceed.
Thanks for that , but unfortunately it is not so clear ( some writings ).