find points laying on the circle $\displaystyle x^2 +y^2 -4x -2y =0 $ at which the tangents to the circle have slope = 0.5

i get the answer :

points are : (3,-1) (3,3) (1,3) (1,-1)

i have a guide answer (3,-1) (1,3) only .... Is this a mistake in the guide answer ???

Thanks in advance