Pre Algebra Periods 1, 2, & 4

AREA Sections 10-1, 10-2 & 10-3

All these formulas are related to the basic concept of A = bh
Where the perimeter/circumference fenced in my puppy, the area of the yard will tell me how much sod (grass) I should buy to stop the puppy's paws from getting muddy!

Area of rectangles and parallelograms 10-1

A = (base)(height)
In a parallelogram, whether it's a rectangle, rhombus, square or other parallelogram
A = bh with the height being a line perpendicular to both bases (not the slanted side!)
You have learned the area of a rectangle as A = lw, but the l = b and the w = h
You may have learned the area of a square as A = s² , but that's because the b = h


Area of triangles 10-2
A = (1/2)(base)(height or altitude)
Any parallelogram can be split into 2 triangles using a diagonal.
Because of this, the area of a triangle is half that of a parallelogram.

A = ½bh

Area of trapezoid = (average of the 2 bases)(height)
A = ½(b₁+ b₂)h

Just add the two bases together and divide by 2—that’s the average!!

Then multiply by the height

A trapezoid has 2 bases that ARE NOT EQUAL. So which base is THE base?
If you use the smaller base, you won't have enough sod for your yard and the puppy's paws are still getting muddy.
If you use the larger base, you'll have too much sod for your yard and the extra will rot.
Sooooooooo..... you actually need to take the average of the two bases times the height
A = (average of the 2 bases)(height)
A = (b₁ + b₂) h
theitheis2

Area of Circles 10-3
Area of circle = (Pi)(r²)

If you are given the diameter remember to take half of the diameter to find the radius and make sure to square the radius!!

Use 3.14 or 22/7 as a good approximation of pi. Remember pi is irrational—never ending and never repeating