a) Ta có: $(SCD)\cap (SAE) = \left\{S\right\}$
Trong mp $(ABC)$, gọi $\left\{M\right\}=AE\cap CD$
$M\in AE;\, AE\subset (SAE)\Rightarrow M\in (SAE)$
$M\in CD;\, CD\subset (SCD)\Rightarrow M\in (SCD)$
$\Rightarrow (SCD)\cap (SAE)=\left\{M\right\}$
Vậy $(SCD)\cap (SAE) = SM$
b) Ta có:
$(SCD)\cap (BFC)=\left\{C\right\}$
Trong mp $(SAB)$, gọi $\left\{N\right\}=BF\cap SD$
$N\in BF;\, BF\subset (BFC)\Rightarrow N\in(BFC)$
$N\in SD;\, SD\subset (SCD)\Rightarrow N\in(SCD)$
$\Rightarrow (SCD)\cap (BFC)=\left\{N\right\}$
Vậy $(SCD)\cap (BFC) = CN$
