In an ordered pair, the x-coordinate comes first and the y-coordinate comes second. To reflect a point in the y-axis, we use the same y-coordinate and take the opposite of the x-coordinate.
Practice makes perfect
We want to graph the point N(1,-3) on the coordinate plane. Then, we want to reflect it across the y-axis.
Graphing the Point
In an ( x, y) ordered pair, the first number tells us the x-coordinate of the point and the second number tells us the y-coordinate of the point. To graph N( 1, -3), we first find 1 on the x-axis and remember this grid line. The x-coordinate 1 tells us to move 1 unit to the right of the origin — the positive horizontal direction.
Next, we find -3 on the y-axis and follow this grid line until it collides with the grid line from our x-coordinate. The y-coordinate -3 tells us to move 3 units down from the origin — the negative vertical direction.
The point N( 1, -3) lies on the point at which these two grid lines intersect.
Graphing the Reflection
We want to reflect a point in the y-axis of a coordinate plane. We need to follow two rules to do this.
To reflect a point in the y-axis, we use the same y-coordinate and take the opposite of the x-coordinate.
Let's reflect the given point N(1,-3) in the y-axis.
We can see that the point is located at N'(-1,-3) after the reflection.
