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# Constructing angles

Sal uses a protractor to create 10° and 155° angles. Created by Sal Khan.

## Want to join the conversation?

• who invented the protractor?
• Joseph Huddart invented the protractor. I looked it up :)
• Angles as we know it can go up to 360, 540 and so on. But can there be a negative angle?
• Yes. Positive angles are measured counterclockwise, starting at Quadrant 1 in the Coordinate plane.
Negative angles are measured clockwise, so, for example, an angle of - 30 degrees would be the same size as an angle of + 30 degrees, but would lie in Quadrant 4 instead of Quadrant 1.
• I know how to use the protractor. I'm giving the correct answer but It's showing wrong
• ya miscalculated i'll help you right after i get my last black hole bage
• I am STUCK. So I did the same exact thing as the hint every single time, but it counted me wrong EVERY SINGLE TIME. Anyone have any suggestions? Is it a technical situation, or am I wrong? I have moved the protractor and the angle to the middle of the dot, and did the angles 180 degrees and followed the angles, but it still does not work.
• DON'T LISTEN TO THE HINTS ask the TEACHER for HELP
(1 vote)
• is it possible to measure a 3d shape?
• Yes it is! For a three dimensional shape, (consider a sphere or ball) you can measure its volume, you can measure its diameter, and you can measure its circumference. You can also measure its weight or mass.
(1 vote)
• why is a side have a line
• how do I beat khan academy?
• You can't
(1 vote)
• domain expansion malevolent shrine