# Complement and supplement of an angle

• Jan 17th 2011, 06:28 PM
IDontunderstand
Complement and supplement of an angle
Can -42 degrees have a complement and/or supplement?

I do not think that it can happen. my angle is in the third quadrant. So I cannot make that a positive angle that I can add another angle to to make 90 degrees or 180 degrees. So I believe that this cannot have a complement or supplement.

Thus can -330 degrees have a complement and/or supplement?

It is 30 degrees so 60 degrees will give me 90 degrees is my logic correct?

Thank you
• Jan 18th 2011, 12:19 AM
emakarov
This depends on the precise definitions of angles, complementary angles and supplementary angles. There are at least three variants.

(1) An angle is just a number. Then, of course, there exist solutions to the equations -42 + x = 90 and -42 + x = 180.

(2) An angle is a geometric figure on a plane consisting of two rays with a common beginning. Then it does not make sense to talk about angles whose measure is negative.

(3) This is like (2), but we fix a direction of the positive rotation on the plane (say, counterclockwise) and designate which of the angle's sides is the first and which is the second. Then the angle's measure is considered positive if the first side, rotated by that measure in the positive direction, coincides with the second side. Geometric addition of angles should be made more specific by saying that we make the second side of the first angle coincide with the first side of the second angle.

In (3), every angle has a complementary and a supplementary angle. For example, a complementary angle to -42 is 132.

Quote:

I do not think that it can happen. my angle is in the third quadrant.
I think -42 lies in the fourth quadrant.