Tentukan bayangan y=x2 - 4 oleh pencerminan terhadap garis y = -1

(x,y) —Ref[y=-1]—› (x',y') = (x, 2(-1)-y)
• x' = x
• y' = -2-y → y = -2-y'
Maka,
y = x² - 4
(-2-y') = (x')²-4
-y' = x'² - 2
y' = 2 - x'²