Point d is the image of d(-2,1) under a reflection across the x-axis. what are the coordinates of d?

(-2,-1)

Step-by-step explanation:

To reflect something across an axis we need to change the coordinate of the other axis.  To reflect a point across the X axis we need to change the sign on  the Y axis because that will put it on the other side of the X axis.  In this question the 1 is what we will change from positive to negative.  By doing this it will move the point from above the X axis to below the X axis.

I hope this helps and please don't hesitate to ask if there is anything still unclear!