abc is a triangle and ab=bc and bp-bq show that ap=cq using euclids axiom or postulates.
AB=AC
AP+BP=AQ+CQ
(BY AXIOM 3 THINGS WHICH R EQUAL TO ONE ANOTHER IS EQUAL TO ONE ANOTHER)
AP+BP-BP=AQ+CQ-AQ
AP=CQ
HENCE PROVED
AP+BP=AQ+CQ
(BY AXIOM 3 THINGS WHICH R EQUAL TO ONE ANOTHER IS EQUAL TO ONE ANOTHER)
AP+BP-BP=AQ+CQ-AQ
AP=CQ
HENCE PROVED