根据图片上的题目，求圆的半径，解题过程需配合图进行展示---**Extraction Content:** **Question Stem:** 求圆的半径? **Other Relevant Text:** r = ? **Chart/Diagram Description:** * **Type:** Geometric figure (Circle with internal lines and labels). * **Main Elements:** * **Circle:** A circle is shown. * **Center:** A black dot is located at the center of the circle. * **Lines:** Two red line segments originate from the center. * One segment extends horizontally to the left from the center towards the circumference and is labeled with the number "10". * The other segment extends vertically upwards from the center towards the circumference and is labeled with the number "5". * **Angle:** A right angle symbol is shown at the center, indicating that the horizontal and vertical red line segments are perpendicular to each other. * **Labels:** The horizontal segment is labeled "10". The vertical segment is labeled "5". * **Background:** A faint brain-like image is visible within the circle in the background. * **Watermarks:** Repetitive watermarks "头条 @有点东西" are present throughout the image.