各位師兄可唔可以教下我做樓上個題 ~
應該係同 angle in alt. segment / tangent prop. 個 d 有關
謝解答

a) proof ABC and PBD are similar triangle first

b) PB=PD and PB+ PA = AC (isso tri)

(a) Joining OD,
OD=OC (radii)
Angle ODC= Angle OCD=x ( base angles, isos. triangle ODC)

Angle AOD=2X (ext. angle, triangle OCD)

Joining PO,
Angle AOP=Angle POD=x (tangent properties)

Since AB=AC,
Therefore angle ABC = angle ACB= x (base angles, isos triangle ABC)

angle PDB= angle POD =x (angle in alt. segment)

Since angle PBD=x=angle PDB
Therefore PB=PD (sides opp. equal angles)

(b) Since AC is the diameter,
AC=AB=PA+PB(given),
PB=PD (proved in (a)),
Therefore, PA+PD is equal to the diameter of the circle.