Whenever a ray of light passes parallel to the principal axis it will always pass through its focus.
The focus is a point where all rays of light after reflection meets or appears as they are meeting ( in fig). It is denoted by F.
It can be seen in the attached figure that the ray of light is passing parallel to the principal axis and after reflection it pass through its focus.
t2 equal the displacement of the particle over the same time period if t2> t/2? hint: consider a sine wave starting at t1=0, then consider a closing wave starting at t1=0, for your explanatio
this could be newton#'s law of cooling. the cooling curve is exponential