3rd Grade Math
Geometry
Unit 5
Quadrilaterals
A quadrilateral is any four-sided figure. Some quadrilaterals include squares, rectangles, rhombuses, trape
Triangles
Triangles are figures that have exactly three sides and three angles.There are three types of triangles.
Polygons
A polygon is a plane figure with at least three straight sides and angles, and typically five or more.
Types of Triangles
Equilateral Triangles
All 3 sides and angles are equal
Isosceles Triangles
2 sides and 2 angles are equal
Scalene Triangles
No sides or angles equal
Types of Quadrilaterals
There are more types of quadrilaterals than just these, but here are 3 examples!
Square
4 Equal Sides and 4 Right Angles
Rhombus
4 Equal Sides and at least 2 equal angles.
Rectangle
4 Equal Right Angles and parallel sides.
Shapes and Fractions
You can also divide shapes into equal parts to visualize fractions! What fractions do you see in the picture to your right?
ROW 1: 1/2 ... 1/4 ... 1/3
ROW 2: 1/2 ... 6/12 ... 1/4
ROW 3: 1/5 ... 2/4 ... 3/5
Finding The Area of Certain Shapes
In order to find the area of a rectangle, you would multiply its base times its height. Looking at the rectangle on the right, it has a base of 5 units, and a height of 3 units. So, by multiplying 5 and 3, you get that the area of the rectangle is 5 x 3 = 15 units!
Try counting the number of units in the rectangle to see for yourself!
Think of finding the area of the rectangle like this: there are 5 columns each with 3 units in each group. What does that sound like? Multiplication! So, there are 5 groups of 3 or 5 x 3 units in the rectangle.
Measurement and Geometry
What is perimeter?
Perimeter is the total distance around a shape or place. You can find the perimeter of a shape by adding up all the lengths of all the sides.
The perimeter of a shape can be found by adding up the length around the outside of the shape.
This particular shape is a pentagon, meaning it is a shape with 5 sides.
In this case, when we add up all the sides, we find that the perimeter of the shape is 8 + 8 + 10 + 7 + 10 = 43 units!
What is Area?
Area is the amount of space that a flat surface takes up. For squares and rectangles, you can find the area by multiplying the length times the width (the measurement of two of the sides). For example, for a rectangle with side lengths 3 and 5, the area would be 15 because 3 x 5 = 15.
Don't get discouraged by how many different shapes and names that all of the shapes have!
There are lots of similarities between shapes that can help you!
Also, focus on the names of the shapes themselves, they have meanings that can give you clues to what the shape looks like!
