Question

If a point P(–2, 1) is reflected across the line x = –1, what are the coordinates of its reflection image?

Answer 1

A couple things to consider:
What kind of a line is x=-1? It's vertical, right? That means that the reflected image will keep the same y-value as the original. Think about it; the points will have the same height if you flip it across a vertical line.

Answer 2

Second thing to consider:
If a point is being reflected across x=-1, the new point must be as far away from the axis of reflection as the old point, right? We know that an x-value of -2 is 1 unit away from the line x=-1. Therefore, the new point's x-value must also be 1 unit away from x=-1. So this new x-value has to be 0. Does that make sense?