Tam Ngô's Profile

Hạ $BE\perp SC$ tại $E$

gọi $O$ là giao điểm $AC,BD$

$SA\perp BD,AC\perp BD\Rightarrow \left(SAC\right)\perp BD$

$\Rightarrow BD\perp SC$

mà $BE\perp SC$

$\Rightarrow \left(BDE\right)\perp SC\Rightarrow DE\perp SC$

$\Rightarrow$ góc giữa 2 mp $\left(SBC\right),\left(SDC\right)=\widehat{BED}=2\widehat{BEO}$

$\tan \widehat{BEO}=\frac{OB}{OE}=\frac{OC}{OE}=\frac{1}{\sin {60}^{\circ }}=\frac{2\sqrt{3}}{3}$

$\Rightarrow \widehat{BED}=2\arctan \left(\frac{2\sqrt{3}}{3}\right)$