Question

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Point B(-2,4) lies on a circle centered at A(1, 3). Write a paragraph proof to determine whether C(4, 2) also lies on the circle.
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Answer 1

I am given that the center of a circle is at A(1, 3) and that point B(-2, 4) lies on the circle. Applying the distance formula to A and B, I get the following:

AB=Square Root ( (-2 - 1 )^2 + (4 - 3 )^2 ) = Square root ( 9 + 1 )

AB = Square root (10)

Since B lies on the circle, this length is the length of the radius of the circle. Applying the distance formula to A and C(4, 2), I get the following:

AC = Square Root ( ( 4 - 1 )^2 + (2 - 3 )^2 ) = Square root ( 9 + 1 )

AC = Square root (10)

Thus, the distance to C from the center A is equal to the length of the radius of the circle. Any point whose distance from the center is equal to the length of the radius lies on the circle. Therefore, point C lies on the circle.

Explanation:

Answer 2

Answer: see proof below

Explanation:

The standard equation of a circle is (x - h)² + (y - k)² = r² where (h. k) is the center of the circle and r is the radius. It is given that A (h, k) = (1, 3) and point B (x, y) = (-2,4) is on the circle. Substitute the center (h, k) and point B(x, y) = (-2,4) into the standard equation of a circle to get r² = 10. To prove that C(x, y) = (4, 2) is also a point on the circle, substitute the center (h, k) and the point C(x, y) = (4, 2) into the standard equation of a circle to get r² = 10. Since the radius is the same for both point B and point C and it is given that point B is on the circle, then we must conclude that point C is also on the circle.