What is the image of (-1, 1) when reflected across the line y = x?

Answer 1

Sketch the situation, and you'll be able to figure it out pretty easily. (-1,1) is in Quadrant 2. Sketch in y=x. Now draw a line segment that starts at (-1,1) and hits the line perpendicularly. Now continue on the same distance past the line. You'll see that you end up at (1,-1), which is the image of the original point.

You could also take the instructions y=x to mean that you should substitute the y value for the x and vice versa. So, for any point reflected across this line, just switch the coordinates.

Best wishes!