Question

A student states that the reflection of triangle ABC across the y-axis is triangle A’B’C’. Determine if the student is correct or has made an error. <:)

Answer 1

Answer: The student is not correct

To reflect over the y axis, you use this rule

$(x,y) \to (-x,y)$

The x coordinate swaps in sign (from positive to negative, or vice versa) while the y coordinate stays the same.

So for a point like A(1,1), it should move to A ' (-1, 1) and not (-2,1) like the diagram shows.

B(3,1) should move to B ' (-3, 1)

C(1,4) should move to C ' (-1, 4)

It appears that the student applied a reflection over the y axis, and then they shifted the triangle 1 unit to the left.