Search IntMath
Close

450+ Math Lessons written by Math Professors and Teachers

5 Million+ Students Helped Each Year

1200+ Articles Written by Math Educators and Enthusiasts

Simplifying and Teaching Math for Over 23 Years

# The ASA Criterion for Triangle Congruence

In geometry, two figures are congruent if they have the same size and shape. When we talk about the size and shape of a figure, we are referring to its angles and sides. There are three possible ways that two triangles can be congruent: AAA, SAS, and SSS. Today, we're going to focus on the ASA criterion.

The ASA criterion states that two triangles are congruent if they have two angles and one side in common. In other words, if we know that angle A equals angle B, and angle C equals angle D, and side AC equals side BD, then we can say that triangles ABC and CDE are congruent.

It's important to note that the ASA criterion only works if the given information is accurate. For example, let's say we know that angle A equals angle B, and angle C equals angle D, but side AC does not equal side BD. In this case, we cannot say that triangles ABC and CDE are congruent.

Let's look at an example to see how the ASA criterion works in practice. Suppose we have two triangles, ABC and DEF. We know that angles A and B are both 60 degrees, and that angles C and D are both 90 degrees. We also know that side AC is 10 centimeters long, and side DE is 15 centimeters long. Based on this information, can we say that triangles ABC and DEF are congruent?

Yes! We can use the ASA criterion to conclude that these two triangles are indeed congruent. Angle A equals angle B because they are both 60 degrees. Angle C equals angle D because they are both 90 degrees. Side AC is 10 centimeters long, while side DE is 15 centimeters long—but since these sides are corresponding sides (meaning they occupy the same position in each triangle), we can multiply 10 by 3 to get 30 centimeters. This tells us that side AC is indeed congruent to side DE. Therefore, based on the information given, we can conclude that triangles ABC and DEFare congruent using the ASA criterion.

## Conclusion:

The ASA criterion is a way to determine whether or not two triangles are congruent. To use the ASA criterion, you need to know that two angles and one side in each triangle must be equal. If you have this information—and it must be accurate—you can then conclude that the two triangles in question are indeed congruent. Try using the ASA criterion on some practice problems to get a feel for how it works!

## FAQ

### How do you prove ASA criteria?

There are a few steps involved in proving ASA criteria. First, you'll need to label the angles and sides of each triangle. Then, you'll need to state which angles and sides are equal. Once you've done that, you can use a series of algebraic equations to prove that the triangles are indeed congruent.

### What is ASA used for geometry?

The ASA criterion can be used to determine whether or not two triangles are congruent. To use the ASA criterion, you need to know that two angles and one side in each triangle must be equal. If you have this information—and it must be accurate—you can then conclude that the two triangles in question are indeed congruent.

### Explain the ASA criterion proof in geometry.

The ASA criterion states that two triangles are congruent if they have two angles and one side in common. In order to prove this, you'll need to label the angles and sides of each triangle. Then, you'll need to state which angles and sides are equal. Once you've done that, you can use a series of algebraic equations to prove that the triangles are indeed congruent.

### What is the SAS criterion?

The SAS criterion states that two triangles are congruent if they have two sides and one angle in common. In order to use the SAS criterion, you need to know that two sides and one angle in each triangle must be equal. If you have this information—and it must be accurate—you can then conclude that the two triangles in question are indeed congruent. You can also use the SAS criterion to prove that two triangles are congruent.