# supplementary angle vs complementary angle

#### Audrey_V

##### New Member
Hello!

I am trying to understand the underlying difference between two words 'supplementary' and 'complementary', which are both used to describe angles. Two acute angles are called complementary if their measurements add up to 90 degrees. Two angles are called supplementary when either both are right angles, or one is obtuse and another is acute. In fact both words mean that one angle's measure is added to another to get 90 degrees in case of complementary ones, or 180 degrees in case of supplementary ones. I will appreciate your help on finding the answer about that underlying meaning that makes these two words different.

Thank you!

• #### Keith Bradford

##### Senior Member
Take two angles, A and B.
If A+B=90°, they are complementary.
If A+B= 180° they are supplementary.

That's all there is to it.

#### Audrey_V

##### New Member
Take two angles, A and B.
If A+B=90°, they are complementary.
If A+B= 180° they are supplementary.

That's all there is to it.
Oh, I understand the math! I don't understand the nuances of the meaning of these two words; they both sound the same to me, in both cased we add another angle to get 90, or 180 degrees.

#### JulianStuart

##### Senior Member
Oh, I understand the math! I don't understand the nuances of the meaning of these two words; they both sound the same to me, in both cased we add another angle to get 90, or 180 degrees.
In one case, to get to 90°, we use the word complementary. In the other case, we use a different word to get to a different number of degrees: 180°. They are clearly not the same

#### Audrey_V

##### New Member
In one case, to get to 90°, we use the word complementary. In the other case, we use a different word to get to a different number of degrees: 180°. They are clearly not the same
Good. I understand they are not the same, that is why I came here to ask you who they differ. I would like to see the nuances in the meaning of these words (not the math) that make them different. So it is a question about the English language

#### JulianStuart

##### Senior Member
Good. I understand they are not the same, that is why I came here to ask you who they differ. I would like to see the nuances in the meaning of these words (not the math) that make them different. So it is a question about the English language
You mean: both complementary and supplementary refer to increasing the value of the angle? The different words are used specifically in a geometry context so we know which is meant, 90 or 180. English (and I suspect other languages) can use a given word in a general sense/context, or in a specific, llimited sense in a specific context - in this case, geometry. Outside that specific situation, complementary means "completing" in some way, while supplementary just means additonal (with regard for the resulting total). If I were in a geometry class I would understand the words differently than if I were in some other class or situation.

#### JulianStuart

##### Senior Member
Good. I understand they are not the same, that is why I came here to ask you who they differ. I would like to see the nuances in the meaning of these words (not the math) that make them different. So it is a question about the English language
In addition to the links to definitions helpfully provided above, you can find that information on this very forum - enter the word in the search box at the top of each page - it will take you to the definitions provided by two dictionaries and a list of threads in which the name occurs in the title. (See my sig!) Try it You will also find this one supplementary [complementary] treatment where the nuance is discussed a little

#### Audrey_V

##### New Member
In addition to the links to definitions helpfully provided above, you can find that information on this very forum - enter the word in the search box at the top of each page - it will take you to the definitions provided by two dictionaries and a list of threads in which the name occurs in the title. (See my sig!) Try it You will also find this one supplementary [complementary] treatment where the nuance is discussed a little
I see. Thank you very much!

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