∆ABC was transformed according to the rule (x, y) → (x, −y) to create ∆A'B'C'. What transformation justifies the relationship between the triangles?

Question

 A translation 1 unit to the right and 1 unit down justifies ∆ABC ≅ ∆A'B'C'. A rotation of 90° counterclockwise justifies ∆ABC ≅ ∆A'B'C'. A reflection over the x-axis justifies ∆ABC ≅ ∆A'B'C'. A reflection over the y-axis justifies ∆ABC ≅ ∆A'B'C'.

Answer 1

Here's a suggestion.

Pick a pair of numbers, say (4, 5). Plot it.

Now transform that pair, (4 -5). Plot it.

What did you see?

Answer 2

When a point is reflected over the x-axis, the x-coordinate is unchanged and the y-coordinate is negated.