Chapter 1.5 relating
to Chapter 2
There are 2 formulas in Geometry that are used with
equations a great deal:
Perimeter and area
PERIMETER – the sum of all the sides of a
polygon
AREA- ( we are only focusing on squares,
rectangles and triangles)
Area of a square = s2
where s represents the length of the square
Area of a rectangle = bh or lw
Area of a triangle = bh/2
or ½ bh
(We discussed how we were able to arrive at the formula for
a triangle…)
Compound Shapes
Sometimes a shape will be composed of several shapes. Right
now we are covering shapes that are composed of squares rectangles and
triangles. You break the shape into the parts you know. IF there is a side
missing a measurement, you may have to SUBTRACT or ADD using the known measurements
of other sides.
We looked at Page 24…
In Chapter 2 you will use the formula to find a missing side
using equation solving!
If you know the area of a rectangle is 20 feet squared and
one of the sides is 2 feet, what is the other side?
Since A = bh you can
solve for the missing side by plugging in the area and the known side
20 = 2h
h = 10
10 feet
An example of a triangle
The area of a triangle is 20 feet squared. The base of the
triangle is 10 feet. How long is the height?
A = b/2
20 = 10h/2
20 = 5h
h = 4
The height must be 4 feet
Always remember the formula of a triangle is half the
formula for a rectangle with the same base and height!
This one works nicely because the base was even and we could
divide by 2 easily. You can also solve triangles with a base or height that is
odd—but we will focus on that later with 2-step equations and equations with
fractional coefficients.
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