Notes 1.2 Perimeter and Area in the Coordinate Plane

Area in the Coordinate Plane

Geometry

​Learning Target:

Find areas of polygons in the coordinate plane.

Polygons

​In geometry, a figure that lies in a plane is called a plane figure.

​

​Polygon - a CLOSED plane figure that is formed by three or more line segments (called sides).

​A polygon is named by listing the vertices in consecutive order.

​Convex & Concave

​Convex - a line drawn through 2 consecutive points does NOT go through the interior

​

​Concave - a line drawn through 2 consecutive points goes through interior

​Identifying Polygons

​Recall that polygons can be identified by the number of sides.

​

​While some polygons have special names, in general they are named by the number of sides followed by "-gon."

​

​Ex: 13 sides is called 13-gon

​Perimeter and Area Formulas

​or

​P = a + b + c

​A=1/2 bh

​P = S + S+ S + S

A = S²

​P = 2L + 2W

​A = LW

​Ex) Find perimeter and area of polygon (Square)

​Ex) Find perimeter and area of Polygon (Triangle)

​First use distance formula to find the length of the horizontal segment.

​Ex) Find perimeter and area of Polygon (Triangle)

​Ex) Find perimeter and area of Polygon (Triangle)

​A = 21 units

​Let's Practice

Multiple Choice

What is the area of the rectangle?

• 28 units squared

• 45 units squared

• 33 units squared

• 19 units squared

Multiple Choice

What is the area of the figure? 

• 11 square units

• 15 square units

• 25 square units

• 30 square units

Multiple Choice

What is the perimeter (in units) of the triangle formed by the points (-3,1), (-3,5), and (4,1)?

• 65

• 8.06

• 14

• 19.06

Multiple Choice

Square ABCD has vertices A(-2,-3), B(4, -1), C(2, 5), and D(-4, -3). What is the area of the square?

• $$2\sqrt{10}$$

• $$4\sqrt{10}$$

• 40

• 20

Multiple Select

A polygon has the coordinates (-5,0) (5,0) (5,-5) (-5,-5) Find the area AND the perimeter. Choose both answers.

• area = 30 units²

• area = 50 units²

• perimeter = 50 units

• perimeter = 30 units

Multiple Select

Which triangles has an area of 22.5 square units?

Select all that apply.

Exit Ticket. Find the Perimeter and Area of this Polygon