AC=BC
AP∗BQ=AC2
∠CAB=∠CBA (base angles of isosceles triangle)
∠CAB+∠CAP=180° (linear pair)
∠CAP=180°−∠CAB------(1)
also:
∠CBA+∠CBQ=180° (linear pair)
∠CBQ=180°−∠CBA------(2)
from 1 and 2 we get:
∠CAP=∠CBQ
given: AP∗BQ=AC2
⟹APAC=ACBQ
⟹APAC=BCBQ
⟹AP=BQ
Therefore by SAS: ΔACP∼ΔBCQ