Question 1005166
The radius is 4.5 km, so a radian is 4.5 km, and the skier went 1.8 km or 0.45 radian before taking a rest.
x^2+y^2=20.25 (r^2)
The sine of 0.45 radian is 0.4350.  Multiply that by 4.5 to get the y-value,1.9575
The cosine of 0.45 radian is 0.9004.  Multiply that by x, 4.5, to get 4.052.  That is the the x-value
(4.052,1.9575)
That is done because the sine is x/radius.
The two coordinates squared and added=20.25.