The image of the point (0,0) about the line x+y+1=0 is .
If the image of (X1,Y1) w.r.t ax+by+c=0 is (x,y), then
x−X1a=y−Y1b=−2(aX1+bY1+c)a2+b2
Here, x−01=y−01=−2(1)2 ⇒(x,y)=(−1,−1)