→ 1/2PRS = 1/2PQR QTRSir , my query is how is half of angle PRS = ha

This question was asked in Ex 6.3, 6

→ 1/2PRS = 1/2PQR QTR

Sir , my query is how is half of angle PRS = half of angle PQR angle QRT? Since angle QRT is not included in triangle PQR . Please help..