Let ABC be a triangle with \A < 60度. Let X and Y be the points on the sides AB and AC, respectively, such that CA+AX = CB +BX and BA+AY = BC +CY . Let P be the point in the plane such that the lines PX and PY are perpendicular to AB and AC, respectively. Prove that \BPC < 120度.

令ABC為一三角形,角A小於60度.
令X及Y分別為AB及AC上一點.並使CA+AX = CB +BX,BA+AY = BC +CY.
令平面上一點P,使PX及PY分別垂直於AB及AC
證明角BPC小於120度

以上應該沒錯吧