Solve for k: X^2 + (y - k)^2 = 21 Subtract X^2 from both sides: (y - k)^2 = 21 - X^2 Take the square root of both sides: y - k = sqrt(21 - X^2) or y - k = -sqrt(21 - X^2) Subtract y from both sides: -k = sqrt(21 - X^2) - y or y - k = -sqrt(21 - X^2) Multiply both sides by -1: k = y - sqrt(21 - X^2) or y - k = -sqrt(21 - X^2) Subtract y from both sides: k = y - sqrt(21 - X^2) or -k = -sqrt(21 - X^2) - y Multiply both sides by -1: Answer: k = y - sqrt(21 - X^2) or k = sqrt(21 - X^2) + y
