Q21: 图是一个坐标轴，坐标中心O为原点，画了一个半径为50的圆。还有一点P在坐标为(50,0)的位置。很简单的。
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. A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient. B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient. C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient. D. EACH statement ALONE is sufficient. E. Statements (1) and (2) TOGETHER are NOT sufficient. 这道题目答案是A, 可我认为是D。 因为知道Q在圆上，即知道Q到原点O的距离QO=50。通过直角三角形勾固定律 (1) 知道Q的横坐标，一定可以推出Q的纵坐标=50^2-(-30)^2； (2)知道Q的纵坐标，一定可以推出Q的横坐标=50^2-(-40)^2； 最后一定可以算出PQ的呀。 | 
