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.

### Course: Algebra 2 (Eureka Math/EngageNY)>Unit 2

Lesson 2: Topic A: Lessons 8-10: Trigonometric graphs and radians

Sal determines the quadrant at which a ray falls after a rotation by a certain measure of radians.

## Want to join the conversation?

• Would it be quicker to just to convert from radian to degrees?
• I believe the point of the video is to get you to start thinking of the unit circle in terms of radians. Yes, you can convert to degrees, but it is good to have a feel for radians. Knowing that 90° = π/2 and 180° = π, and etc. will be very useful for solving problems in many disciplines.
• At he writes the value of pi = 3.14, but Sal uses it as a reference for radians, isn't the 3.14 value in degrees? I mean he says that 3 radians is close to 3.14. So basically I'm asking what measure are we using in normal arithmetic, degrees right? If so, how come he compared 3 radians to 3.14 ,what are presumebly, degrees? Please tolerate any ignorance you come across in my question, I'm simply trying to understand the concepts.
• Pi is simply a mathematical constant. It does not have any default units attached to it. The number 5 is not in degrees or meters, it is just the number 5. The same with pi.
• I'm really confused

I thought 2pi=360° so pi is 180° and so if you move 3pi you will do 360 +180 degrees respectively or one rotation and a half but Sal puts it in the second quadrant

Can someone explain what I did wrong
• Notice that there is a difference between 3 and 3pi. 3pi would indeed take you past 360 degrees, but 3 is a little less than just 1pi--thus putting it in quadrant 2.
• At around he says "pi/2 here would be 3.5 pi over 7". I have no clue what he means by that.
• He's trying to figure out if 2pi/7 is less than or greater than pi/2. By multiplying the numerator and denominator of pi/2 by 3.5, he gets 3.5pi/7. 3.5 is greater than 2, so 3.5pi/7 (or pi/2) is greater than 2pi/7, which means 2pi/7 would not pass pi/2 which puts it in the first quadrant.
• , why is 90 degrees equal to pi/2 radians?
• I feel like I get it but at the same time I feel like I don't...
• At shouldn't the terminal side rest on the on the line since 1 radian is a 180 degrees (Straight Line) and 2 radians (Full rotation). And if it has 3 radians shouldnt it be a full rotation and a straight line?
It is π radians that equals 180°
• Sal said that pi radians= 180 degrees then can i say that 3.14 radians = 180 degrees?Help would be appreciated.

thank you
• Pretty much, yes.... if you want to be "nit-picky" about it, 3.14 radians = 179.90875 degrees. In general, it's better to use pi instead of a rounded approximation like 3.14 or 22/7 or something like that.

By the way, 22/7 radians = 180.07245 degrees.
• If we rotate a ray π radians counter-clockwise, we'll get the ray lying on the x-axis.