Tentukan bayangan lingkaran x^2+y^2+4x-2y-4=0 rotasi R [0 -90°]

rotasi R (o,-90) = (y,-x)
x' = y --> y = x'
y' = -x --> x = -y'

x^2+y^2+4x-2y-4=0
(-y')^2+(x')^2+4 (-y')-2 (x')-4=0
y^2+x^2-4y-2x-4=0