Shapes
All two-dimensional shapes that have three or more sides (not circles) are also known as polygons.
SQUARE
to find the area multiply the height and width or the side with itself A = H X W or A = L X W or A = s2
to find the perimeter... add all the sides or multiply all four sides
P = s + s + s + s or P = 4 X s = 4s
DIAMOND
please note that this diamond is simply a tilted square
therefore the same rules and formulas apply
RECTANGLE to find the area multiply the height and width
A = H X W or A = L X W
to find the perimeter add all the sides
P = s + s + s + s or P = 2( H + W )
TRIANGLES
to find the area of a triangle note that we use
half of the area of a rectangle
A = ½ X ( H X W )
with certain shapes we use the terms base and height
and therefore we use the formula...
A = ½ x B x H or A = B X H or A = b • h
2 2
to find the perimeter of a triangle we simply
add all of the sides
P = Side 1 + Side 2 + Side 3
CIRCLE
note that the height is measured with a 90° angle from the base
essentially the height is measured perpendicularly to the base
( a 90° angle is also known as a right angle )
before calculating the area of a circle we must introduce the idea of pi
Pi ( π ) = 3.14159... or π = C
d
C = circumference ( think of it as the perimeter of the circle )
C = π x d or C = 2 x π x r
d = diameter: a line across the middle and from edge to edge
d = 2 x r
r = radius: a line that goes from the middle to the edge of a circle
r = ½ x d or r = d or r = d ÷ 2
2
to find the area of a circle multiply pi by the square of the radius
A = π x r2
this video is a great way to remember the terminology for calculating with circles
( it is just under two minutes long )
Enjoy !!!
and to a get a peek into the
awesomeness of pi ... take
a look at the Pi video found
in the youtube menu options
mmmmmm.... pi
Other common shapes ...
(the following are all polygons ~ so are triangles, squares, and rectangles)
PARALLELOGRAM
The word parallel means two lines along side of each otherand continue without ever meetingTo find the area... multiply the base by the height
A = b x h
TRAPEZOID
b
To find the area... multiply the height with the sum of the two bases and then divide the result by two A = h x ( b + B ) or h x ½ (b + B)
2
B
more common shapes...
(don't forget the perimeter is found by adding all the sides together)
Pentagon Hexagon Octogon
( 5 sides ) ( 6 sides ) ( 8 sides )
regular shapes (like the ones shown here) have all sides that equal each other
and the lesser known decagon (10 sides)
