Circles Basics and Equations

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Questions and Answers

What is the standard form of the equation of a circle centered at (4, -1) with a radius of 7?

  • (x + 4)^2 + (y - 1)^2 = 49
  • (x - 4)^2 + (y - 1)^2 = 7
  • (x - 4)^2 + (y + 1)^2 = 49 (correct)
  • (x + 4)^2 + (y + 1)^2 = 7

What is the center of the circle given by the equation x^2 + y^2 - 6x - 10y + 18 = 0?

  • (6, 10)
  • (-3, -5)
  • (3, 5) (correct)
  • (4, -2)

What is the radius of the circle represented by the equation (x - 3)^2 + (y - 5)^2 = 16?

  • 2
  • 8
  • 16
  • 4 (correct)

Which of the following forms indicates that an equation represents a circle?

<p>x^2 + y^2 = r^2 (C)</p> Signup and view all the answers

What is the first step in converting the equation x + y + 6x - 7 = 0 into standard form?

<p>Combine like terms (B)</p> Signup and view all the answers

What is the center of the circle described in the equations provided?

<p>(-2, 2) (C)</p> Signup and view all the answers

What is the radius of the circle that has the center (-2, 2)?

<p>5 (B)</p> Signup and view all the answers

Which equation correctly represents the circle with radius 4 and centered at (0, 0)?

<p>16 (D)</p> Signup and view all the answers

Which form is used to express the circle equation in the form (x-h)² + (y-k)² = r²?

<p>25 (A)</p> Signup and view all the answers

In which quadrant would the center (-2, 2) of the circle lie?

<p>2 (C)</p> Signup and view all the answers

If the equation of the circle is (x + 3)² + (y - 1)² = r², what is the y-coordinate of the center?

<p>1 (D)</p> Signup and view all the answers

How would you represent the radius of a circle in the equation format (x - h)² + (y - k)² = ?

<p>5 (B)</p> Signup and view all the answers

What is the value of r² in the equation of the circle (x - 2)² + (y + 1)² = r² when r = 6?

<p>36 (D)</p> Signup and view all the answers

What is the center of the circle represented by the equation $(x + 5)^2 + (y - 2)^2 = 49$?

<p>(-5, 2) (C)</p> Signup and view all the answers

What is the radius of the circle defined by the equation $(x + 5)^2 + (y - 2)^2 = 49$?

<p>7 (A)</p> Signup and view all the answers

Using the distance formula, what is the distance between the points P1(-5, 3) and P2(7, 11)?

<p>$14$ (C)</p> Signup and view all the answers

What is the midpoint between the points P1(-5, 3) and P2(7, 11)?

<p>(1, 7) (B)</p> Signup and view all the answers

What is the slope of the line that passes through the points P1(2, 3) and P2(5, 11)?

<p>$\frac{8}{3}$ (C)</p> Signup and view all the answers

Which of the following equations represents a circle with center (2, -1) and radius 6?

<p>$(x - 2)^2 + (y + 1)^2 = 36$ (B)</p> Signup and view all the answers

From which form can the equation of a circle be derived?

<p>Standard form (D)</p> Signup and view all the answers

If a circle has a radius of 7 and is defined by the equation $(x + 6)^2 + (y - 1)^2 = 49$, what is the center of the circle?

<p>(-6, 1) (A)</p> Signup and view all the answers

Which of the following statements is true regarding the slope of vertical lines?

<p>Their slope is always undefined. (A)</p> Signup and view all the answers

What is the general form of the equation of a circle centered at (h, k)?

<p>$(x - h)^2 + (y - k)^2 = r^2$ (A)</p> Signup and view all the answers

Which equation represents a circle centered at the origin with a radius of 4?

<p>$x^2 + y^2 = 16$ (D)</p> Signup and view all the answers

What is the correct equation of the circle with a center at (0, 3) and a radius of 5?

<p>$x^2 + (y - 3)^2 = 25$ (D)</p> Signup and view all the answers

Given the equation of the circle $x^2 + (y + 2)^2 = 36$, what is the center of the circle?

<p>(0, -2) (D)</p> Signup and view all the answers

If a circle has the equation $(x - 1)^2 + (y + 4)^2 = 49$, what is its radius?

<p>7 (D)</p> Signup and view all the answers

What is the standard equation of the circle whose center is (1, 7) and radius is $2 \sqrt{13}$?

<p>$(x - 1)^2 + (y - 7)^2 = 52$ (A)</p> Signup and view all the answers

Determine the coordinate point that is 6 km away from the station located at (0, -4).

<p>(±6, -4) (C)</p> Signup and view all the answers

Which equation represents the possible locations of an epicenter 1 km from the shore?

<p>$x^2 + (y + 4)^2 = 36$ (B)</p> Signup and view all the answers

What are the possible coordinates of the epicenter if it is 1 km away from the shore?

<p>(±3.31, 1), (±5.2, -1) (A)</p> Signup and view all the answers

How does the distance formula relate to determining the radius of a circle in the context of an earthquake epicenter?

<p>It generates the radius used in the standard circle equation. (D)</p> Signup and view all the answers

What does the center of a circle represent in relation to the epicenter of an earthquake?

<p>The starting point of the seismic activity. (A)</p> Signup and view all the answers

What is the radius of the circle used to denote the possible epicenter locations?

<p>6 km (C)</p> Signup and view all the answers

What is the significance of the endpoint coordinates (-5, 3) and (7, 11) in determining the radius and center of the circle?

<p>They are part of the diameter used to locate the center. (B)</p> Signup and view all the answers

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Study Notes

Circles Basics

  • A circle consists of all points equidistant from a fixed center point, with distance referred to as the radius.
  • The standard equation format for a circle centered at ((h, k)) is ((x - h)^2 + (y - k)^2 = r^2).
  • For a circle centered at the origin, the equation simplifies to (x^2 + y^2 = r^2).

Example Circle Equations

  • Circle with center at (0, 0) and radius 5:
    (x^2 + y^2 = 25).

  • Circle centered at (0, 3) with radius 6:
    ((x - 0)^2 + (y - 3)^2 = 36) simplifies to (x^2 + (y - 3)^2 = 36).

Finding the Standard Form

  • To convert the equation of a circle into standard form, complete the square for (x) and (y).
  • Example: For the equation (x^2 - 8x + y^2 + 2y - 32 = 0), complete the square to yield: ((x - 4)^2 + (y + 1)^2 = 49).

Center and Radius Extraction

  • Given the equation (x^2 + y^2 - 6x - 10y + 18 = 0):

    • Complete the square to find center at (3, 5) and radius as 4 units.
  • For (4x^2 + 4y^2 + 12x - 4y - 90 = 0):

    • Center is at ((-2, 2)) with a radius of 5 units.

Graphing Circles

  • A circle can be graphed using its center and radius on a Cartesian plane.
  • Example: For center (2, -1) and radius 6, graph the equation ((x - 2)^2 + (y + 1)^2 = 36).

Distance and Slope Formulas

  • The distance formula between two points ((x_1, y_1)) and ((x_2, y_2)) is calculated as: (d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}).

  • The slope of a line through points (P_1(x_1, y_1)) and (P_2(x_2, y_2)) is defined as: (m = \frac{y_2 - y_1}{x_2 - x_1}).

Problem Solving Applications

  • For a circle determined by the endpoints of a diameter, calculate the center and radius using the midpoint and distance formulas.
  • An example involving seismic data can be described through the equation of circles related to distance from a given location.

Conic Sections

  • Circles are one type of conic section formed by the intersection of a plane and a cone.
  • Their shapes are defined by the angle at which the cone is sliced, creating different conic sections like ellipses, parabolas, and hyperbolas.

Summary of Methods

  • Completing the square, extracting the center and radius, and graphing circles are fundamental methods in understanding and applying circle equations in problems related to geometry and real-world scenarios.

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