This is a series of THREE lessons that build on each other where we first learn how to find the area of parallelograms, then the area of right triangles, and lastly the area of triangles.
Jump to:
Area of parallelograms
Area of right triangles
Area of triangles
Learn WHY the area of a parallelogram is calculated as base times height (altitude).
The formula is A = b × h and it is really simple to prove. If we cut a triangle off of one end of a parallelogram and move it to the other end, we get a RECTANGLE, whose area is the same as the based of the parallelogram times its height.
We also practice finding the areas of parallelograms, and draw a parallelogram with a given area.
This geometry lesson is meant for 6th grade, and is one in a series of lessons on area of polygons. Our next step is the area of right triangles, followed by the area of triangles.
This is a leadup lesson to the lesson about the area of triangles. In this lesson we only deal with RIGHT triangles. It is easy to see their area is HALF of the area of the rectangle drawn around the triangle.
We find the areas of some right triangles and the area of a compound shape. Lastly, the task is to DRAW a right triangle with a given area (300 square centimeters). I show how to find the base and the height for this triangle and draw 2 different ones.
We learn how the area of any triangle is HALF of the area of the corresponding parallelogram, and that is the reason for the formula A = bh/2 (base times height divided by two).
We also find the area of some triangles that are drawn in the grid.
Classify triangles — video lesson
Math Mammoth Geometry 2 — a selfteaching worktext with explanations & exercises (grades 67)
Back to the geometry videos index
Math Mammoth TourConfused about the different options? Take a virtual email tour around Math Mammoth! You'll receive: An initial email to download your GIFT of over 400 free worksheets and sample pages from my books. Six other "TOURSTOP" emails that explain the important things and commonly asked questions concerning Math Mammoth curriculum. (Find out the differences between all these differentcolored series!)This way, you'll have time to digest the information over one or two weeks, plus an opportunity to ask me personally about the curriculum. A monthly collection of math teaching tips & Math Mammoth updates (unsubscribe any time) We respect your email privacy.
Note: You will FIRST get an email that asks you to confirm your email address. If you cannot find this confirmation email, please check your SPAM/JUNK folder. 
"Mini" Math Teaching CourseThis is a little "virtual" 2week course, where you will receive emails on important topics on teaching math, including:
 How to help a student who is behind You will also receive: A GIFT of over 400 free worksheets and sample pages from my books right in the very beginning. A monthly collection of math teaching tips & Math Mammoth updates (unsubscribe any time)We respect your email privacy.
Note: You will FIRST get an email that asks you to confirm your email address. If you cannot find this confirmation email, please check your SPAM/JUNK folder. 
Maria's Math TipsEnter your email to receive math teaching tips, resources, Math Mammoth news & sales, humor, and more! I tend to send out these tips about once monthly, near the beginning of the month, but occasionally you may hear from me twice per month (and sometimes less often). Peek at the previous tips here. You will also receive:
We respect your email privacy.
