План: 1)RM 2)RM(ABC)? a)RMЄBB 1 C 1 б)(ABC)(BB 1 C 1 )=BC в) RMBC 1 =X 1 3) RMCC 1 =X 2 4)PX 1 ;PX 2 PX 1 AD=X 3 X 1 X 3 AB=X 4 5)PX 2 (A 1 B 1 C 1 )? а)PX 2 Є DD 1 C 1 б)(A 1 B 1 C 1 )(DD 1 C 1 )=D 1 C 1 в)PX 2 D 1 C 1 =X 5 6)X 5 RA 1 B 1 =X 6 X 4 X 6 AA 1 =X 7 7)X 6 X 3 RX 2 PX 3 X 7 X 6 – искомое сечение Х4Х4 А В D R C A1A1 B1B1 C1C1 X6X6 P X1X1 D1D1 X5X5 X2X2 X3X3 X7X7 13