Bunuel wrote:
A circle has a center of (1, 2) and passes through (1, –3). The circle passes through all of the following EXCEPT:
A. (–4, 2)
B. (–3, 5)
C. (0, 6)
D. (4, –2)
E. (5, 5)
Kudos for a correct solution.
The coordinates of any point through which a circle passes must satisfy the general equation of a circle:
\((x - h)^2 + (y - k)^2 = r^2\), where \(r\) is the circle's radius and \((h, k)\) are the coordinates of the circle's center.
In this case, the equation is \((x - 1)^2 + (y - 2)^2 = r^2\)
Because we are given one point, we can find the value of the squared radius easily by substituting the x and y coordinates of the given point (1, -3) into the equation:
\((1 - 1)^2 + (-3 - 2)^2 = r^2\)
\(0^2 + (-5)^2 = r^2\), or \(25 = r^2\) such that by substitution back into the general equation
\((x - 1)^2 + (y - 2)^2 = 25\)
Now just plug the coordinates from the answer choices in to see if they satisfy the equation.
(A) (-4, 2) yields \((-4 - 1)^2 + (2 - 2)^2\)=
25 + 0 = 25 KEEP
(B) (-3, 5) yields\((-3- 1)^2 + (5 - 2)^2\) =
16 + 9 = 25. KEEP
(C) (0, 6) yields \((0 - 1)^2 + (6 - 2)^2\)=
1 + 16 = 17. REJECT
(D) (4, -2) is the mirror image of A (and yields 9 + 16 = 25) KEEP
(E) (5, 5) yields (5 - 1)^2 + (5 - 2)^2 =
16 + 9 = 25. KEEP
Answer C
I'm not a fan of the distance formula.
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