All points along the circle with be the distance of the radius from the center...so the radius can be found using the Pythagorean Theorem..
r^2=(4-1)^2+(6-2)^2
r^2=9+16
r^2=25
r=5
The equation of the circle can be expressed as:
r^2=(x-h)^2+(y-k)^2 where (h,k) correspond to the center of the circle, (2,1) in this case.
(x-2)^2+(y-1)^2=25
if you wanted it in a more standard form...
(y-1)^2=25-(x-2)^2
(y-1)^2=25-x^2+4x-4
(y-1)^2=-x^2+4x+21
y-1=(-x^2+4x+21)^(1/2)
y=1(+/-)(-x^2+4x+21)^(1/2)
5>x because you can subtract 5 from both sides and 3x from both sides
All it takes for a relation to be a function is for each possible first number of a pair there's only one possible second number.
So if any of the sets has two pairs with the same first number, that one's not a function.
The last one has (3,2) and (3,5) so isn't a function.
