这道题目怎么解---```plain 3、如图，平面直角坐标系中，直线AB与x轴交于点A(-3, 0)与y轴交于点B(0, 6)，点C是直线AB上的一点，坐标为(m, 4)，经过点C作直线CD//x轴交y轴于点D. (1) 求点C的坐标； (2) 已知点P是直线CD上的动点， ①若△POC的面积为4，求点P的坐标； ②若△POC为直角三角形，请求出所有满足条件的点P的坐标. Chart Description: Type: Planar Cartesian coordinate system with points and lines. Two identical diagrams are provided, the second labeled as "备用图" (Spare diagram). Main Elements: - Coordinate Axes: X-axis and Y-axis intersecting at the origin O. Arrows indicate positive directions. Labels 'x' and 'y' are present. - Line AB: A straight line passes through a point A on the negative x-axis and a point B on the positive y-axis. - Points: - Point A is labeled on the negative x-axis. - Point B is labeled on the positive y-axis. - Point O is the origin. - Point C is labeled on the line AB, in the second quadrant relative to the origin. - Point D is labeled on the positive y-axis, above O. - Line CD: A horizontal line segment is drawn from point C to point D. It is explicitly stated and shown that CD is parallel to the x-axis and intersects the y-axis at D. - Labels and Annotations: Points A, B, C, D, O, x, y are labeled. The second diagram is labeled "备用图". - Relative Position and Direction: A is on the negative x-axis. B is on the positive y-axis. C lies on the line segment implicitly defined by A and B (or the line passing through A and B). CD is horizontal, so C and D have the same y-coordinate. D is on the y-axis, so its x-coordinate is 0. Based on the diagram, C is to the left of D, and D is above O. C appears to be in the second quadrant, and D is on the positive y-axis. ```