Question

You reflect triangle PQR, with vertices P(-2, -4), Q(-3,-1), and R(-4,-4), across the y-axis to get triangle P’Q’R’. What are the coordinates of triangle P’Q’R’?

Answer 1

Rule: to reflect any point across the vertical y axis, we simply flip the sign of the x coordinate. If the x coordinate is positive, we flip to negative, and vice versa.

P starts at (-2,-4)
Reflect P over the y axis and we end up with (2,-4). Note how the y coordinate stays the same. The x coordinate flipped from negative to positive.

Repeat for point Q
Q = (-3,-1) becomes Q ' = (3,-1)

and finally for point R
R = (-4,-4) turns into R ' = (4,-4)

So we have these three new points
P'(2,-4)
Q'(3,-1)
R'(4,-4)

Final Answer: Choice D

Side note: connect any point with its reflection and the two points form a flat horizontal line. The horizontal line is perpendicular to the mirror line which is the vertical y axis.