∆abc is reflected about the line y = -x to give ∆a'b'c' with vertices a'(-1, 1), b'(-2, -1), c(-1, 0). what are the vertices of ∆abc?

The rule of reflection over the line y = -x ⇒ (x,y) → (-y,-x)

The coordinates of the image :
A'(-1, 1), B'(-2, -1), C'(-1, 0)
so, the coordinates of ABC is 
A( -1,1) , B(1,2) and C(0,1)