Across what line of reflection was the angle reflected in the coordinate plane below?

Let us revise the reflection

If point (x , y) reflected across the x-axis, then its image is (x , -y)

If point (x , y) reflected across the y-axis, then its image is (-x , y)

If point (x , y) reflected across the line y = x, then its image is (y , x)

If point (x , y) reflected across the line y = -x, then its image is (-y , -x)

∵ Point A (-5 , 8) is reflected across the line y = x

∵ If point (x , y) reflected across the line y = x , then its image is (y , x)

∵ x = -5 and y = 8

- Switch x and y

∴ The image of point A is A' = (8 , -5)