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# Equation practice with supplementary angles

Given the algebraic expressions that represent a pair of supplementary angles, Sal forms and solves an equation. Created by Sal Khan.

## Want to join the conversation?

• At Sal says, "And I'll assume it's in degrees." What other angle measurements are there, if any at all?
• There are two other measures of a turn of a circle. There are radians, and there are gradians. 1 radian is equivalent to the ratio of the circle's circumference to its diameter, also known as 2*pi, and gradians is equal to the ratio of the circle's circumference to its diameter, divided by 400; therefore a gradian is equivalent to 1/400 of a turn in a circle, 9/10 of 1 degree, or pi/200 of a radian.
• Lines AB and CD intersect at M. If the m∠AMD = 2x + 20 and the m∠DMB = 3x + 60, find the measure of ∠AMC.
• hi sal, i want to tell you can you add missing numbers in equations
• What is the difference between radians and degrees?
• Radians are a different way to measure angles.
I always remember there are 2*pi radians in a circle, which is also equals 360 degrees
So, one radian = 360 degrees/(2*pi) = 57.3 degrees
You'll use radians quite a bit in trigoinometry
• How can we assume it forms a line based on how it looks? Shouldn't it be specified in the question?
• I agree. I took geometry last year and the one thing that we had to "assume" sometimes was that a line was not two rays. Is that what you mean? I think that if the line is clearly straight then you can just assume that it is a line.

Hope this helps!!
• What is a supplementary angle compared to a complimentary angle?
(1 vote)
• Complementary angles add up to 90 degrees. Graphically, if they were put together, they would form a right angle.
Supplementary angles add up to 180 degrees. Graphically, if they were put together, they would form a straight angle.
• I'm told to determine the supplementary angle of a given edge with an improper fraction example 34 7/16 how do I go about that
• While your use of "a given edge" does not make any sense with determining supplementary angles, if your angle has a fraction such as 7/16, you subtract 180 - 34 = 146, then borrow one from that, so 145 + 1 - 7/16 = 145 + 16/16 - 7/16 = 145 9/16 degrees.
• why is my question not being approved if ur supposed to answer them?
• because someone flagged it, I guess?
(1 vote)
• How do you know if and angle is supplementary in a figure when it only has one found degree
• Supplementary means all angles add up to 180, right? Which means, if you know one degree (one angle) and there are 2 angles, then you know that the other angle is 180 minus the angle you already know.

For example, lets say that one angle is 20. There are two angles with a sum of 180. Since ONE angle is 20, the other MUST be 160, because that is the only thing that adds up to 180.
Equation format: x + y = 180
x = First angle that you are trying to find
y = Second angle you are trying to find
These two numbers MUST equal 180.