16Hit1600
Geometry and TrigonometryVery hardHighest point of a circle tangent to the x-axis

Geometry and Trigonometry practice question

In the xy-plane, a circle with centre (3, 4) is tangent to the x-axis. What is the y-coordinate of the highest point on the circle?

Answer: 8

Tangent to the x-axis means the radius equals the centre's distance from that axis, 4. The highest point is 4 above the centre, at y = 8.

Common wrong answers

If you answered 0
0 is the point of tangency.
If you answered 4
4 is the centre's y-coordinate, or the radius.
If you answered 7
7 adds the centre's x-coordinate to the radius.

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