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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. Circle C has center (2, −3) and is tangent to the y-axis. What is the radius of the circle?

    Answer: 2

    The distance from the center (2, −3) to the y-axis (x = 0) is |2| = 2, which equals the radius.

  2. A circular pizza with diameter 16 inches is cut into 8 equal slices. What is the area of each slice?

    Answer: 8π

    Total area = π(8)² = 64π. Each slice = 64π/8 = 8π square inches.

  3. A circle is inscribed in a square with side length 10. What is the area of the region inside the square but outside the circle?

    Answer: 100 − 25π

    The inscribed circle has radius 5. Its area = 25π. Area outside = 100 − 25π.

  4. In a circle, an arc measures 4π and the radius is 6. What fraction of the circle's circumference does this arc represent?

    Answer: 1/3

    Circumference = 2π(6) = 12π. Fraction = 4π/12π = 1/3.

  5. A circle with center O has points A and B on it. The central angle AOB = 120° and OA = 9. What is the length of chord AB?

    Answer: 9√3

    Using the law of cosines: AB² = 9² + 9² − 2(9)(9)cos(120°) = 81 + 81 − 162(−1/2) = 162 + 81 = 243. AB = √243 = 9√3.

  6. What is the equation of the circle with center (0, 0) that passes through (−3, 4)?

    Answer: x² + y² = 25

    Radius = √((−3)² + 4²) = √(9+16) = 5. Equation: x² + y² = 25.

  7. The area of a circle is increased by 44%. By what percentage is the radius increased?

    Answer: 20%

    New area = 1.44πr². New radius = √(1.44)r = 1.2r. The radius increases by 20%.