Act Math Practice

Coordinate Geometry Answer 1

Coordinate Geometry Answer 1:

1. If a circle with center (-6, 6) is tangent to the x axis in the standard (x, y) coordinate plane, what is the diameter of the circle?

A. -6

B. -12

C. 6

D. 12

E. 36

The correct answer is D.

REMEMBER: If the center of a circle (x, y) is tangent to the x axis:

1) The point of tangency is equal to (x, 0) and
2) The distance between (x, y) minus (x, 0) is equal to the radius.

The center of this circle is (-6, 6) and the point of tangency is (-6, 0).

So we need to subtract these two coordinates in order to find the length of the radius:

(-6, 6) - (-6, 0) = (0, 6)     In other words, the radius length is 6.

Also remember this formula:

diameter length = radius length ´ 2
diameter length = 6 ´ 2
diameter length = 12

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