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### Course: Basic geometry and measurement>Unit 7

Lesson 3: Points in all four quadrants

# Points on the coordinate plane examples

The coordinate plane is a two-dimension surface formed by two number lines. One number line is horizontal and is called the x-axis. The other number line is vertical number line and is called the y-axis. The two axes meet at a point called the origin. We can use the coordinate plane to graph points, lines, and more. Created by Sal Khan and CK-12 Foundation.

## Want to join the conversation?

• why do you have to start with the y axis than the x axis first

• Always start with X then Y I like to think of it alphabetically.
• Is there a reason that we use the "X" axis first?
• Yes. When plotting points, we start with the number we start with (the independent variable, x), then we use the number we end with (the dependent variable, y). The independent variable is always first, so we use the x axis first.
• at about how come Sal only puts four dash marks on his coordinate plane instead of more when he could have easily fit more than that?
• just because he can't fit every single solitary number into one small screen
• Was Descartes the one who taught the convention that the x comes first in (x,y)?

• Rene Descartes is credited for the introduction of Cartesian geometry, so it should be safe to say he is the one who fostered the convention that x comes before y. Also it makes sense since x comes before y in the alphabet.
• why cant the x axis go up and down and why cant the y axis go side to side
• The way that axes work is just our convention. If you want a q-axis and an m-axis, then be my guest. X is usually used to refer to a horizontal direction/motion, and Y refers to vertical. This is just the way some person thought of it, and this is the way we've been doing it for the past hundreds of years.
• why are the quadrants counter clockwise?
• Some of these things are simply named by convention, but I also think it may have something to do with the way that we "sweep out" angle in trigonometry; clockwise from the positive x-axis. I'm not really sure if that's why, but it seems applicable.
• At , are quadrants important?
• Definitely! If you're given a problem, and even in real life, quadrants can help determine that where you plotted the coordinates is correct. It sort of narrows down the options!!
• If I use the Y axis first will I be incorrect or will my number be backward?