1)(x-5)²+(y+1)²=26-F r=√(26-F) (5,-1)到3x-y+4=0的距离为√(26-F) d=|3*5-(-1)+4|/√(3²+1²)=√(26-F) => 20=√[10(26-F)] => 400=260-10F ∴ F=-142)(x-1)²+(y+2)²=16 r=4 弦心距d=|1-2-3|/√(1²+1²)=2√2 ∴|AB|=2√(r²-d²)=2√(16-8)=4√2