21 In the figure shown, the circle has center O and radius 50, and point P has coordinates (50,0). If point Q (not shown) is on the circle, what is the length of line segment PQ ?
(1) The x-coordinate of point Q is – 30.
(2) The y-coordinate of point Q is – 40.
--> i got D, 因為半徑已知
不懂為何答案是A
--> 请問on the circle 是在圓上的意思嘛?
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