Math Problem Statement

Find the radius of a circle that passes through the points (5, 0), (8, 1), and (6, 0).

Solution

To find the radius of the circle passing through the points (5,0)(5, 0), (8,1)(8, 1), and (6,0)(6, 0), we need to determine the center of the circle first, and then calculate the radius. Here's the step-by-step solution:

Step 1: General Equation of a Circle

The general equation of a circle is: (xh)2+(yk)2=r2(x - h)^2 + (y - k)^2 = r^2 where (h,k)(h, k) is the center of the circle and rr is the radius.

Step 2: Set up the System of Equations

Since the circle passes through the points (5,0)(5, 0), (8,1)(8, 1), and (6,0)(6, 0), we can plug these points into the circle equation:

  1. For (5,0)(5, 0): (5h)2+(0k)2=r2(5 - h)^2 + (0 - k)^2 = r^2

  2. For (8,1)(8, 1): (8h)2+(1k)2=r2(8 - h)^2 + (1 - k)^2 = r^2

  3. For (6,0)(6, 0): (6h)2+(0k)2=r2(6 - h)^2 + (0 - k)^2 = r^2

Step 3: Simplify the Equations

Expand each of the equations:

  1. (5h)2+k2=r2(5 - h)^2 + k^2 = r^2 2510h+h2+k2=r225 - 10h + h^2 + k^2 = r^2

  2. (8h)2+(1k)2=r2(8 - h)^2 + (1 - k)^2 = r^2 6416h+h2+12k+k2=r264 - 16h + h^2 + 1 - 2k + k^2 = r^2 6516h2k+h2+k2=r265 - 16h - 2k + h^2 + k^2 = r^2

  3. (6h)2+k2=r2(6 - h)^2 + k^2 = r^2 3612h+h2+k2=r236 - 12h + h^2 + k^2 = r^2

Step 4: Eliminate r2r^2 by Subtracting Equations

Subtract equation 1 from equation 3: (3612h+h2+k2)(2510h+h2+k2)=0(36 - 12h + h^2 + k^2) - (25 - 10h + h^2 + k^2) = 0 Simplifying: 112h=0    h=112=5.511 - 2h = 0 \implies h = \frac{11}{2} = 5.5

Subtract equation 1 from equation 2: (6516h2k+h2+k2)(2510h+h2+k2)=0(65 - 16h - 2k + h^2 + k^2) - (25 - 10h + h^2 + k^2) = 0 Simplifying: 406h2k=0    6h+2k=40    3h+k=2040 - 6h - 2k = 0 \implies 6h + 2k = 40 \implies 3h + k = 20

Step 5: Solve for kk

Substitute h=5.5h = 5.5 into the equation 3h+k=203h + k = 20: 3(5.5)+k=20    16.5+k=20    k=3.53(5.5) + k = 20 \implies 16.5 + k = 20 \implies k = 3.5

Step 6: Calculate the Radius rr

Substitute h=5.5h = 5.5 and k=3.5k = 3.5 into one of the original equations, say: (55.5)2+(03.5)2=r2(5 - 5.5)^2 + (0 - 3.5)^2 = r^2 Simplify: (0.5)2+(3.5)2=r2    0.25+12.25=r2    r2=12.5(-0.5)^2 + (-3.5)^2 = r^2 \implies 0.25 + 12.25 = r^2 \implies r^2 = 12.5 r=12.5    r=522r = \sqrt{12.5} \implies r = \frac{5\sqrt{2}}{2}

Thus, the radius of the circle is 522\frac{5\sqrt{2}}{2}.

Would you like any further details or have any questions?


Here are five related questions:

  1. How do you find the equation of the circle given three points?
  2. Can the radius be negative?
  3. How does one determine if three points are collinear?
  4. What is the significance of the perpendicular bisectors of chords in a circle?
  5. How would the problem change if one of the points was on the origin?

Tip: For any circle, the perpendicular bisectors of any two chords intersect at the circle's center.

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Math Problem Analysis

Mathematical Concepts

Coordinate Geometry
Circle Equations
System of Equations

Formulas

General Equation of a Circle
Distance Formula
Quadratic Equation

Theorems

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Suitable Grade Level

Grades 10-12