3. In Fig. 6.15, PQR = PRQ, then prove that PQS = PRT.
Given that,
ABC is a triangle such that PQR = PRQ and ST is a straight line.
Now, PQR + PQS = {Linear pair}............(i)
Similarly, PRQ + PRT = ..................(ii)
equating the eq (i) and eq (ii), we get
{but PQR = PRQ }
Therefore, PQS = PRT
Hence proved.