I overheard a student saying, “Why do we need parabolas?” This question is similar to the question why we need percentages.

 

I told him to watch what path a paper ball takes as you throw it into the wastebasket – a parabola. Light is focused to a point by a parabola, hence the satellite dishes are parabolas. Light from a point is focused into a beam by a parabola, hence headlight reflectors are parabolas.

 

SEE THE BOOK FOR MORE DETAILS.

 

The point is that good teaching comes about when the teacher listens to the students and replies to their questioning.