If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

# CA Geometry: Proof by contradiction

4-6, proof by contradiction. Created by Sal Khan.

## Want to join the conversation?

• What do sss aaa sas aas saa mean for being an answer to a question?
• sss=side side side ;sas=side angle side ;aas=angle angle side ;aaa=angle angle angle ;saa=side angle angle
Therefore,sss aaa sas aas saa=7 x side+8 x angle
• In question 5, I understand that the answer would be side-side-side (SSS), but in what situation would you use ASA, SAS, or AAS?
• ASA when you know what 2 angles are, and what the side between the two angles are.
SAS when you know what two sides are and the angle between the two sides are.
And AAS when you know what two angles and one side is but also having the side to where it is not in between the two angle... correct me if i am wrong, i am not to sure about this stuff myself.
• when you have a proof and you need to solve it and or prove something in it right or wrong how would you know which properties or definition of something to use based on the statement?
• what I need is how to solve geometric proofs im having big trouble of how to do proofs like one in the first example.
• I have a Carnegie Learning Textbook for Geometry (volume 1) I cant find the sss aaa aas saa terms in it does anyone know the translation that may be in my textbook because im so confused with proofs. Can anyone help me understand
• After poking around online, I think you might be able to find them in Chapter 5, but with the expanded names (SSS: side-side-side, AAA: angle-angle-angle, AAS: angle-angle-side, and ASA: angle-side-angle).
• I am confused at when Sal says that AB is equal to BC. Didn't the question just say that AB is not equal to BC? Isn't this a contradiction?
• He is contradicting the given statement, showing that the statement AB>BC is false
(1 vote)
• Hi there, could you please help me proof by contradiction "that it is not possible to find a geometric sequence that contains the 3 points t1 = 0.32 t11= 0.41 and t21 =0.54
• what grade level geometry is this? Because this seems a lot easier than the stuff on my tests.
• I learned this is 8th. In my school it's 9th depends on the school and the people in it.
(1 vote)
• What is a contradiction, in general terms?
(1 vote)
• A contradiction occurs when two properties are asserted for something which are not compatible. For example, if you assert that a number is an even number and then later say that it is not an even number, then you have a contradiction.
• Why isn't <a=<c?
(1 vote)
• because it says you can only have two obtuse angles so a=b
(1 vote)
• Can someone explain these Geometry laws.
The Law of Detachment
The Law of Syllobism
(1 vote)
• The law of detachment states that if these two statements are true,

if p then q and p, then you can deduce q.

This means that if you are assured that if a statement p must lead to a conclusion q and you know that p is definitely true, q must also be true.

In an example:
if you are a horse, you have four hoofs
you are a horse
therefore
you have four hoofs
(1 vote)