Question

The equation (x − 1)2 + (y + 1)2 = r2 represents circle J. The point D(0,3) lies on the circle. What is r, the length of the radius of circle J?

Answer 1

`\displaystyle √(17) = r`

Explanation:

According to the Centre-Radius Formula,
`\displaystyle [X - H]^2 + [Y - K]^2 = R^2,`[H, K] represents the centre of the circle, where the negative symbols give the OPPOSITE terms of what they really are, and the radius is ALWAYS squared. So, to find the radius of this circle, you just simply plug the coordinates into the equation:

`(0 - 1)^2 + (3 + 1)^2 = R^2 \\ \\ (-1)^2 + 4^2 = R^2 \\ \\ 1 + 16 = R^2 \\ \\ 17 = R^2 \\ \\ √(17) = R`

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