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 R(-2,5) on the coordinate plane. Then, we want to reflect it across the x-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 R( -2, 5), we first find -2 on the x-axis and make a mental note of this grid line. The x-coordinate -2 tells us to move 2 units to the left of the origin — the negative horizontal direction.
Next, we find 5 on the y-axis and follow this grid line until it collides with the grid line from our x-coordinate. The y-coordinate 5 tells us to move 5 units up from the origin — the positive vertical direction.
The point R( -2, 5) 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 R(-2,5) in the y-axis.
We can see that the point is located at R'(2,5) after the reflection.
