Question

How do you find general form of circle with Center at the point (-3, 1) and tangent to the y-axis?

Answer 1

`(x + 3)^2 + (y - 1)^2 = 3^2`

Explanation:

`(x + 3)^2 + (y - 1)^2 = r^2`

y-axis: `x = 0`

`3^2 + (y - 1)^2 = r^2`

`(y - 1)^2 = r^2 - 9`

`y = 1 ± sqrt {r^2 - 9}`

y is unique only if `r^2 - 9 = 0 Rightarrow r = 3`