Bài 2
Có: \frac{V_{ABCNM}}{V_{SABC}}
= 1 - \frac{V_{SAMN}}{V_{SABC}}
= 1 - \frac{SA}{SA}.\frac{SM}{SB}.\frac{SN}{SC}
= 1 - \frac{1}{1}.\frac{1}{2}.\frac{1}{2} = \frac{3}{4}
\Rightarrow V_{ABCNM} = \frac{3}{4} V_{SABC}
Có:
V_{SABC} = \frac{1}{3}.2a. \frac{a^{2}\sqrt{3}}{4} =...