Question

如图5,PA切○o于点A,割线PBC交○o于点B,C,已知PB=BC=3,AC为直径,则PA的长为多少?

Answer 1

PA和圆相切 → PA⊥OA → PA⊥AC

CO=OA,CB=BP → △COB∽△CAP → ∠COB=∠CAP=90°

OC=OB → AC=AP → △PAC 是等腰直角三角形

PA=PC/√2 =3√2