VSABC / VSAB'C' = (1/3 AK . SSBC) / (1/3 A'H . SSB'C')
( K la hinh chieu cua S len mp ABC. H la hinh chieu cua A len mp SB'C' , binh thuong khi tinh the tich chop SA'B'C' thi ta hay tinh duong cao SH nhung vs bai toan nay ta can tinh duong cao A'H. cong viec nay khong he anh huong den the tich cua chop. vs dg cao A'H thi day se la SB'C') minh nghi cong viec nay k kho vs pan. H se la hinh chieu cua A' len Sk
pan can su dung kien thuc ve ti so the tich nua: vd sABC/SAB'C' = (AB.AC)/(AB'.AC'). tam giac ABC . B' thuoc AB, C' thuoc AC
tu do suy ra
VSABC/VSAB'C' = (AK/A'H) . (SB/SB'). (SC/SC')
= (SA/SA'). (SB/SB'). (SC/SC') dpcm