# Area of Circles / Sectors and Arc Length

In this video I will teach you about the area of a circle, sectors and arc length.  Of course it should go without saying that you want to take excellent notes as there is lots of formulas we will explore.  Did you ever learn how to find the area of a circle?  I assume most of you have used the formula “pi r squared” to find the area of a circle- if not no problem I will cover this in the lesson.  Ok lets give you a quick definition of a few key terms in this lesson.  Circumference is the distance around a circle- think of it as the “perimeter” of the circle.  Sometimes we only want to find a partial distance around a circle- for example a semi-circle.  These “partial circumferences” are called arc lengths.  Now lets apply the same concept to the area of a circle.  A partial area of a circle (think of a slice of pizza) is called a sector.  Make sure you have a good calculator for this lesson as we will be doing a lot of “number crunching”.  Lastly I can’t stress how important it is to practice these formulas if you really want to master the skills- and trust me you do.  Wow!  you have learned so much geometry in this chapter and the entire course.  This is the final lesson of the course and I want to congratulate you if you finished the entire course- you are an amazing student!  I invite you to review all the videos on this site in your effort to master math.  I wish you all the best and thank you for being my student!