A seat in a cinema is found by a row and a seat number. A square on a chessboard is found by a letter and a number. In this course we learn how two numbers fix the position of any point on a flat surface, and how to plot, read and reflect points.
3 lessons, about 1 h 15 min3 simulations10 problems6 practice questionsPython in every lesson
Created by StemPy LabOne number fixes a position on a line. Two perpendicular number lines, the x-axis and the y-axis, fix a position on a flat surface. They meet at the origin, and together they are the Cartesian plane.
A point on the plane is written as an ordered pair x, y. The x-coordinate, or abscissa, is the distance to the right or left of the y-axis, and the y-coordinate, or ordinate, is the distance above or below the x-axis. The order matters. The two axes cut the plane into four quadrants, numbered anticlockwise, with signs plus plus, minus plus, minus minus and plus minus. A point on the x-axis has y equal to 0, a point on the y-axis has x equal to 0, and the origin is 0, 0. A point on an axis is not in any quadrant.
To plot x, y, start at the origin, move x units along the x-axis and then y units up or down, and mark the point. To read a point, look straight down or up to the x-axis and straight across to the y-axis. The reflection of a point in the x-axis changes the sign of y, in the y-axis changes the sign of x, and in the origin changes both. On a line parallel to an axis, the length is the difference of the coordinates taken as positive. Shapes can be drawn from their corners, and the fourth corner of a parallelogram ABCD is A plus C minus B.
Log in to join the discussion.
Loading…