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### Unit 9: Lesson 1

Classify quadrilaterals, including rectangles, rhombuses, and squares.

A quadrilateral is a polygon with four sides.

### Study some examples

Here are some examples of quadrilaterals:
A shape with 4 sides. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line to the right, straight line down, straight line to the left, straight line up and right.
A shape with 4 sides. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line to the right, straight line down, straight line to the left, straight line up.
A shape with 4 sides. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line down and right, straight line down and left, straight line up and left, straight line up and right.

### Try it yourself

Which of the following shapes are quadrilaterals?

Some quadrilaterals go by special names like rectangle, rhombus, and square. Let's learn about them!

## Rectangles

What makes a shape a rectangle?
• There are four right angles.
• There are four sides because it's a quadrilateral.

### Study some examples

Here are some examples of rectangles:
A smaller horizontal rectangle.
A vertical rectangle.
A larger horizontal rectangle.

### Try it yourself

Which of the following shapes are rectangles?

### Challenge problem

Let's consider one more shape:
A shape with 4 equal sides and 4 right angles.

Does the shape have four right angles?

So, is the shape a rectangle?

## Rhombuses

What makes a shape a rhombus?
• All sides are the same length.
• There are four sides because it is a quadrilateral.

### Study some examples

Here are some examples of rhombuses:
A shape with 4 equal sides and no right angles. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line to the right, straight line down and right, straight line to the left, straight line up and left.
A shape with 4 equal sides and no right angles. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line down and right, straight line down and left, straight line up and left, straight line up and right.
A shape with 4 equal sides and 4 right angles. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line to the right, straight line down, straight line to the left, straight line up.

### Try it yourself

Which of the following shapes are rhombuses?

## Squares

What makes a shape a square?
• All sides are of equal length.
• There are four right angles.
• There are four sides because it's a quadrilateral.

### Study some examples

Here are some examples of squares:
A larger shape with 4 equal sides and 4 right angles. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line to the right, straight line down, straight line to the left, straight line up.
A shape with 4 equal sides and 4 right angles. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line down and right, straight line down and left, straight line up and left, straight line up and right.
A smaller shape with 4 equal sides and 4 right angles. The direction of each side is as follows, beginning at the top and continuing in a clockwise pattern: straight line to the right, straight line down, straight line to the left, straight line up.

### Try it yourself

Which of the following shapes are squares?