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Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

A circle in the x y-plane has its center at (-100, 221) and a diameter of 17. Which of the following is an equation of the circle?

A.(x+100)²+(y-221)²=72.25
B.(x+100)²+(y-221)²=289
C.(x-100)²+(y+221)²=72.25
D.(x-100)²+(y+221)²=289

答案和解析

答案：B

解析：

The formula for a circle with a center at (h,k) and a radius of r is: (x-h)²+(y-k)²=r²

The length of the radius is half of the length of the diameter.

1/2*17=8.5

Using the coordinates of the center and the length of the radius of this circle in the equation yields: (x-(-100))²+(y-221)²=8.5²

In standard form, the equation of this circle is: (x+100)²+(y-221)²=72.25