$SM=4MB\Rightarrow SM=\dfrac{4}{5}SB$
$SN=5NC\Rightarrow SN=\dfrac{5}{6}SC$
$\dfrac{V_{SAMN}}{V_{SABC}}=\dfrac{SM.SN}{SB.SC}=\dfrac{2}{3}$
Suy ra $S_{AMNCB}=\dfrac{1}{3}V_{SABC}=3a^3$
Có gì khúc mắc e hỏi lại nhé <3
$SM=4MB\Rightarrow SM=\dfrac{4}{5}SB$
$SN=5NC\Rightarrow SN=\dfrac{5}{6}SC$
$\dfrac{V_{SAMN}}{V_{SABC}}=\dfrac{SM.SN}{SB.SC}=\dfrac{2}{3}$
Suy ra $S_{AMNCB}=\dfrac{1}{3}V_{SABC}=3a^3$ View attachment 197920
Có gì khúc mắc e hỏi lại nhé <3