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# Right angles in shapes (informal definition)

Identify right angles in shapes.

## Introduction

Many shapes have corners. We call a corner a right angle if we can fit a little square perfectly inside it.

### Consider the trapezoid

Let's draw a square in each corner.
In which corners did the little square fit perfectly?
The trapezoid has two right angles.

## Practice

First, let's study some more examples.
Now, try it yourself.
How many right angles are in this square?

How many right angles are in this pentagon?

## Challenge problem

How many right angles does this shape have?

## Want to join the conversation?

• Is a diamond considered a quadrilateral?
• Yes cause it still has 4 sides
• Why do they have to have a right angle?
• It's just one of the 3 main angles in math.
Acute angles are angles that are less than 90 degrees.
Right angles are angles that are exactly 90 degrees.
Obtuse angles are angles that are more than 90 degrees.
You'll work with these three types of angles a lot more as you advance in math.
• I do not get that a petagon have 2 right angls.
• Draw three sides of a square (the bottom line and the two side lines) Then put a peaked roof on it like the roof of a house.

There you have five lines which is the definition of a pentagon (when you see the prefix PENT, that means 5) In this case, you will also see the two right angles where the bottom line and the two vertical lines meet.

Get the idea?
• what is the difference between a rombus and a square?
• A rhombus has 4 sides all of equal length but squares have all equal sides and all 90 degree angles
• Is a quadrilateral just a shape that has four right angles?
• No, a quadrilateral does not need to have 4 right angles. It just needs 4 angles. Think of a trapezoid. This has 4 sides and 4 angles but the angles are not all right angles.
• What is concave?
• Concave, the opposite of convex, describes how a shape is curved. Concave means that a shape curves inward. E.g. in a shape with four (or more) sides, when one of the interior angles is over 180 degrees. You can think of a star - a star has 5 sharp angles that stick outwards AND 5 angle that point inwards. The ones pointing inwards indicate a concave shape.
A function is concave when the second derivative is negative (<0)
• Is a trapezoid considered a quadrilateral?
• Yes, it is a quadrilateral because it has four sides.
And have a good day!
• How many things have right angles?
• Millions of things. Animals can have right angle, cars, humans, and even food.
• Do square has 4 right angles
• yes it does have 4 right angles
• how many right angles can a shape have?