The transformation that matches the triangle in the image is Reflection over the x-axis.
To see this, we can imagine that the original triangle is folded along the x-axis. The resulting triangle will be a reflection of the original triangle, with the same size and shape, but flipped over the x-axis.
The other options do not match the transformation in the image:
Reflection over the y-axis: This transformation would flip the triangle over the y-axis, but the resulting triangle would be different in size and shape from the original triangle.
Rotation 180 degrees: This transformation would rotate the triangle 180 degrees, but the resulting triangle would be different in orientation from the original triangle.
Enlargement: This transformation would enlarge the triangle by a certain factor, but the resulting triangle would be similar to the original triangle, not a reflection of it.
Therefore, the answer is Reflection over the x-axis.