MathDB
TS _|_ SE if SA = SP and TB = TD

Source: 2th XMO (China) Test 2 p1 https://artofproblemsolving.com/community/c3192772_geometry_regional_china

April 7, 2024
geometryperpendicular

Problem Statement

As shown in the figure, BQBQ is a diameter of the circumcircle of ABCABC, and DD is the midpoint of arc BCBC (excluding point AA) . The bisector of the exterior angle of BAC\angle BAC intersects and the extension of BCBC at point EE. The ray EQEQ intersects (ABC)\odot (ABC) at point PP. Point SS lies on PQPQ so that SA=SPSA = SP. Point TT lies on BCBC such that TB=TDTB = TD. Prove that TSSETS \perp SE. https://cdn.artofproblemsolving.com/attachments/c/4/01460565e70b32b29cddb65d92e041bea40b25.png