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Circles Flashcards

7 cards from real Bluebook SAT Test practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the radius of the circle with equation x² + y² = 49?

    Answer: 7

    The standard form x² + y² = r² gives r² = 49, so r = 7.

  2. The center of the circle (x − 3)² + (y + 5)² = 16 is:

    Answer: (3, −5)

    In (x − h)² + (y − k)² = r², the center is (h, k) = (3, −5).

  3. A circle has center (0, 0) and radius 5. What is the circumference?

    Answer: 10π

    Circumference = 2πr = 2π(5) = 10π.

  4. A circle has radius 6. What is its area?

    Answer: 36π

    Area = πr² = π(6)² = 36π.

  5. An arc of a circle with radius 10 subtends a central angle of 90°. What is the arc length?

    Answer: 5π

    Arc length = (θ/360°)·2πr = (90/360)·2π(10) = (1/4)(20π) = 5π.

  6. A central angle of a circle measures 120° and the radius is 9. What is the area of the corresponding sector?

    Answer: 27π

    Sector area = (θ/360°)·πr² = (120/360)·π(81) = (1/3)(81π) = 27π.

  7. An inscribed angle in a circle measures 35°. What is the central angle that subtends the same arc?

    Answer: 70°

    The Inscribed Angle Theorem states the central angle is twice the inscribed angle: 2 × 35° = 70°.