已知两圆的圆心和半径，第三圆的半径，且三圆两两相切，求第三圆圆心坐标

已知两圆的圆心和半径，第三圆的半径，且三圆两两相切，求第三圆圆心坐标。设圆1圆心,半径为 $x_{1}, y_{1}, r_{1}$ , 圆2 $x_{2}, y_{2}, r_{2}$ 。圆3 $x_{3}, y_{3}, r_{3}$ 即可得
1. 公式1.1 $(x_{3} - x_{1})^{2} + (y_{3} - y_{1})^{2} = (r_{3} + r_{1})^{2} = d 31$
2. $(x_{3} - x_{2})^{2} + (y_{3} - y_{2})^{2} = (r_{3} + r_{2})^{2} = d 32$
3. $(x_{2} - x_{1})^{2} + (y_{2} - y_{1})^{2} = (r_{1} + r_{2})^{2} = d 21$
根据1、2、3式即得：
1. $x = (d 21 + d 32 - d 31) / (2 * d 21)$
2. $y = \sqrt{d 32 / d 21 - x^{2}}$