点M是圆的弦的中点,则M与圆心的连线的斜率k=[2－0]/[2－3]=－2,则过M的弦的斜率是k的负倒数,是2,则此弦所在直线的斜率是1/2,又过点M,则y=(1/2)(x－2)＋2即是：x－2y＋2=0