How to Use Number Line Coordinates to Create a Triangle

Creating shapes such as triangles with a number line is a fun and educational exercise for elementary school students. Knowing how to create shapes with number line coordinates will help them solve Cartesian coordinate system problems, which are often taught in middle school. Here, find out how to create a triangle with number line coordinates using two number lines.

Things You'll Need

• 5 grid per inch graph paper
• Pencil and eraser
• Straight edge

Instructions

Number Line and Triangle Construction

1. Construct the number lines. On graph paper, draw two perpendicular number lines of equal length that bisect each other in the center of the page. One line should be parallel to the bottom of the paper and the other to the side of the paper. Label the four quadrants that result from the bisection. Quadrant 1 is the upper right quadrant. Quadrant 2 is the upper left. Quadrant 3 is the lower left and quadrant 4 is the lower right.

2. Label the x- and y-axis. First, label the intersection point of the x- and y-axis as the coordinate (0,0). Then mark equal spaced grid marks on the x-axis and the y-axis. Use the grids on the graph paper as a guide. For each grid mark on the x-axis and to the right of the y-axis, label consecutive whole numbers. Start at 1, then 2, 3, 4 and so forth.

   To the left of the x-axis, use negative whole numbers. For the first grid mark on the x-axis that is immediately to the left of the y-axis, label it -1, for the second, -2, the third, -3 and so forth.

   Label the y-axis grid marks above the x-axis with positive sequential whole numbers. Label the first grid mark, 1, the second, 2, and so forth. For points below the x-axis and on the y-axis, label each grid mark with negative sequential whole numbers. The first y-axis grid mark below the x-axis would be labeled -1, the second, -2, and so forth.

3. Select three x, y coordinate pairs for the three vertexes of the triangle. The three coordinates should not have the same x-coordinate or the same y-coordinates. Such a combination will produce a straight line and not a triangle.

4. Plot the three coordinates. To plot a point, first locate the x-coordinate on the x-axis and then y-coordinate on the y-axis. Draw a line through the x-coordinate on the x-axis that is parallel to the y-axis. Then construct a line parallel to the x-axis that goes through the y-coordinate on the y-axis. Where the two lines intersect will be a point on the triangle.

5. Label each point and draw the triangle. Label the three points A, B and C. Draw a straight line between point A and B. Then draw a straight line between B and C and finally a straight line between C and A. The triangle is complete. Color in the triangle if you like.

Tips & Warnings

• Coordinate pairs with positive x- and positive y-coordinates will be plotted in the first quadrant. Coordinates with a positive x- and negative y-coordinate will be plotted in the fourth coordinate. If both x- and y-coordinates are negative, the point will be in the third quadrant. If the x-coordinate is negative and the y-coordinate is positive, the point will be plotted in the fourth quadrant.

References

• Cartesian Coordinates
• Triangle Animated Construction