30. 已知圆O1:x2+y2+8x+6y+23=0{O_1}:{x^2}+{y^2}+8x+6y+23=0O1:x2+y2+8x+6y+23=0与圆O2:x2+y2−2ax+2by=0{O_2}:{x^2}+{y^2}-2ax+2by=0O2:x2+y2−2ax+2by=0的公共弦所在的直线与直线x+y=0x+y=0x+y=0平行,则a+b=a+b=a+b=___−1-1−1___.