Hello unknown008.
PQR is an equilateral triangle PR =1 T is on QR . A line fromT to PQ is drawn perpendicular to that line meeting it @S ST =TR What length is ST?
By inspection the various angles are
QTS =30 STR=150 TRS=15 PSR=75 PRS=45 SPR= 60
Use the sine rule
1/sin75= SR/sin60 SR=0.897
0.897/sin150= ST/sin15 ST = 0.4643
bjh