remember last weeks activity? first you estimated area - maybe counted squares?? this square has 35...

Remember last weeks activity? First you estimated area - maybe counted

squares??

This square has 35 whole squares and 10 partsquares that are ½ or greater = 40

Then you drew and cut and pasted:

You ended up with a rectangle exactly the same size as this initial parallelogram…

You calculated that the area of the rectangle was 8 x 5 = 40 square units

But we want to be able to calculate area exactly and without having to count squares.

How?

First let’s get used to some new vocabulary:

A rectangle is a parallelogramLength = BaseWidth = Heightl x w is the same as b x h

Notice the height (dotted line)Is perpendicular to, or at a 90° angle with the base.

So… we have a new formula

Area = base x heightA = b x hA = 8 x 5A = 40 u2

Area = base x heightA = b x hA = 8 x 5A = 40 u2

Very important to Remember!!!

• The base and the height must be perpendicular – at a 90° angle with each other.

• Notice that the lateral sides of a parallelogram are NOT perpendicular to the base.

• Thus, a dotted line is drawn to represent the height. Let’s look at a couple examples:

Try this one:

• Use our formula: Area of a parallelogram = Base x HeightA = b x hA = A =

How about this one?