Question

giúp vs

Answer 1

a.

Trong (ABCD) gọi E = \(DM\cap AC\)

Khi đó, \(SE=\left(SMN\right)\cap\left(SAC\right)\)

Trong (SMN), gọi I = \(MN\cap SE\)

Ta có: \(\left\{{}\begin{matrix}I\in MN\\I\in SE,SE\subset\left(SAC\right)\rightarrow I\in\left(SAC\right)\end{matrix}\right.\) \(\Rightarrow I=MN\cap\left(SAC\right)\)