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FF.3 Compare angles to a right angle

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What are angles?

Angles are formed when two rays meet at a point called the vertex. Angles help us describe how open or wide something is.

Examples:
  • A book that is slightly open forms a small angle.
  • A door halfway open forms a larger angle.
  • A corner of a square or rectangle forms a special angle called a right angle.
Note

Angles show how much something turns or opens. The vertex is where the two rays meet.

What is a right angle?

A right angle is an angle that forms a perfect square corner. It measures exactly 90 degrees and looks like the corner of a piece of paper or a book.

Examples:
  • The corner of a classroom whiteboard forms a right angle.
  • The corner of most windows and doors is a right angle.
  • A small square drawn in the corner of an angle shows that it is a right angle.
Note

Look for the “square corner” shape. This is an easy way to tell if an angle is a right angle.

Comparing angles to a right angle

We can compare any angle to a right angle to decide if it is smaller, larger, or the same size. This helps us classify angles quickly and correctly.

Examples:
  • An angle that opens less than a right angle is smaller.
  • An angle that opens more than a right angle is larger.
  • An angle that opens exactly like a right angle is equal to a right angle.
Note

When you compare angles, imagine placing a right-angle corner over them. This helps you see which angle is bigger or smaller.

Angles smaller than a right angle

An angle that is smaller than a right angle opens less than 90 degrees. These angles look narrow or tight.

Examples:
  • The hands of a clock at 2:00 form an angle smaller than a right angle.
  • The corner of a slightly opened book forms a small angle.
  • A slice of pizza with a very thin point shows a small angle.
Note

If the angle looks “sharper” or more closed than a square corner, it is smaller than a right angle.

Angles larger than a right angle

An angle that is larger than a right angle opens more than 90 degrees. These angles look wide or spread out.

Examples:
  • The hands of a clock at 4:00 form a wide angle larger than a right angle.
  • A door opened very wide shows an angle larger than 90 degrees.
  • A scissors opened wide forms a large angle.
Note

If the angle looks more open than a square corner, it is larger than a right angle.

Angles equal to a right angle

An angle that is equal to a right angle is exactly the same size as a right angle. It makes a perfect square corner.

Examples:
  • The corner of graph paper is a right angle.
  • The corner of a standard piece of notebook paper forms a right angle.
  • A right angle is often marked with a small square symbol.
Note

If you can match the angle exactly to a square corner, it is equal to a right angle.

Using comparisons to describe angles

When you compare angles, use clear language such as “smaller than a right angle,” “larger than a right angle,” or “equal to a right angle.” This helps you describe angles accurately.

Examples:
  • “This angle is smaller than a right angle.”
  • “That angle is larger than a right angle.”
  • “These two angles are both equal to a right angle.”
Note

Using the right comparison words helps others understand exactly what kind of angle you are describing.

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