Conic sections practice

Writing equations of circles worksheets

Write exact standard-form circle equations from centers, radii, points, diameters, translations, area, circumference and tangent lines.

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Write each circle equation in standard form.

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Turn geometric facts into standard form

Each worksheet contains ten prompts drawn from centers and radii, three points, translations, diameter endpoints, area, circumference, a point on the circle or a tangent line.

Find the exact center and radius squared first. Then substitute them into (x − h)² + (y − k)² = r².

The separate key gives the exact standard-form equation for every construction.

Learning objective

What this activity builds

Use geometric information to construct an exact circle equation in standard form.

Worked example

Write the equation of the circle with center (2, −3) and radius 5.

(x − 2)² + (y + 3)² = 25.

Substitute h = 2, k = −3 and r² = 25 into (x − h)² + (y − k)² = r².

Teaching notes

Make the practice count

  • Identify the center before finding radius squared.
  • For diameter endpoints, use the midpoint for the center and one quarter of the endpoint distance squared for r².
  • Keep fractional centers and radius squared exact.
  • Check translated centers by applying the stated horizontal and vertical changes.

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Choose one or more construction forms, then change the seed for a reproducible set of ten circle equations.

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Math SheetNameScore/ 10TeacherDateWriting Equations of CirclesUse the given information to write each circle in standard form.1.Write the circle in standard form.x2+y2-81=0Standard equation:2.Center: (9, 11)Radius: 8Standard equation:3.Points: (6, -8), (3, -5), (0, -8)Standard equation:4.Translate by (-4, 1).x2+y2-20·x-4·y-17=0Standard equation:5.Translate by (2, 2).x+92+y+52=36Standard equation:6.Diameter endpoints: (-3, 11) and (3, 11)Standard equation:math-sheet.comPage 1 / 2
Math SheetNameScore/ 10TeacherDateWriting Equations of CirclesUse the given information to write each circle in standard form.7.Center: (-10, -4)Area: 36 pi square unitsStandard equation:8.Center: (-9, 0)Circumference: 2 pi unitsStandard equation:9.Center: (-7, -2)Point on circle: (4, -2)Standard equation:10.Center: (5, -3)Tangent line: x = 8Standard equation:math-sheet.comPage 2 / 2

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