Bluebook SAT Test Circles 1

Question 1

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

Accepted Answer

7

Answer

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

Question 2

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

Accepted Answer

(3, −5)

Answer

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

Question 3

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

Accepted Answer

10π

Answer

Circumference = 2πr = 2π(5) = 10π.

Question 4

A circle has radius 6. What is its area?

Accepted Answer

36π

Answer

Area = πr² = π(6)² = 36π.

Question 5

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

Accepted Answer

5π

Answer

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

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