Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
8. Perimeter, Circumference, and Area
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Exercise 54 Page 66

In order to find the side lengths of the polygon use the Distance Formula and, to find the area, separate the polygon into small rectangles and a triangle.

Perimeter: 32+3sqrt(2) units
Area: 49.5 units square

Practice makes perfect

We will draw a polygon ABCDEFG with the following vertices. A(1,1), B(10,1), C(10,8), D(7,5), E(4,5), F(4,8), G(1,8) Let's plot these points on the coordinate plane and connect them to draw the polygon.

Now, we will find the lengths of the polygon by using the Distance Formula. XY=sqrt(( x_1- x_2)^2+( y_1- y_2)^2) In the formula, XY is the distance between the points X and Y, ( x_1,y_1) is the coordinates of X, and ( x_2,y_2) is the coordinates of Y. Now, let's find the length of each side of the polygon ABCDEFG by applying the formula. We will substitute the points A(1,1) and B(10,1), to find the length AB to start.
AB=sqrt((x_1-x_2)^2+(y_1-y_2)^2)
AB=sqrt(( 1- 10)^2+( 1- 1)^2)
AB=sqrt((-9)^2+(0)^2)
AB=sqrt(81+0)
AB=sqrt(81)
AB=9
Thus the length AB is 9 units. We can find the other lengths in the same way.
Side Coordinates sqrt((x_1-x_2)^2+(y_1-y_2)^2) Length
AB A( 1,1) and B( 10,1) sqrt(( 1- 10)^2+( 1- 1)^2) AB=9
BC B( 10,1) and C( 10,8) sqrt(( 10- 10)^2+( 1- 8))^2) BC=7
CD C( 10,8) and D( 7,5) sqrt(( 10- 7)^2+( 8- 5)^2) CD=3sqrt(2)
DE D( 7,5) and E( 4,5) sqrt(( 7- 4)^2+( 5- 5)^2) DE=3
EF E( 4,5) and F( 4,8) sqrt(( 4- 4)^2+( 5- 8)^2) EF=3
FG F( 4,8) and G( 1,8) sqrt(( 4- 1)^2+( 8- 8)^2) FG=3
GA G( 1,8) and A( 1,1) sqrt(( 1- 1)^2+( 8- 1)^2) GA=7
Finally, we can find the perimeter of the polygon ABCDEFG by adding all seven sides of it together.
P=AB+BC+CD+DE+EF+FG+GA
P=9+7+3sqrt(2)+3+3+3+7
P=32+3sqrt(2)
Thus, the perimeter is 32+3sqrt(2) units. Next, we will find its area by separating it into small rectangles and a triangle as the following.

We will find the area of each rectangle A_R and the area of the triangle A_T by using the formulas. A_R= b h and A_T= b h/2 In the formula, b is the base and h is the height.

Area Base Height A=bh or A=bh/2 Result
A_1 b=3 h=7 A_1= 3* 7 21
A_2 b=3 h=4 A_2= 3* 4 12
A_3 b=3 h=4 A_3= 3* 4 12
A_4 b=3 h=3 A_4=3* 3/2 4.5
Finally, we can find the total area A by adding the smaller areas together.
A=A_1+A_2+A_3+A_4
A=21+12+12+4.5
A=49.5
Thus, the area of the polygon is 49.5 units square.