S△ABC=∣xA×(yB−yC)+xB×(yC−yA)+xC×(yA−yB)∣2S_{\triangle ABC}=\frac{|x_{A}\times(y_{B}-y_{C})+x_{B}\times(y_{C}-y_{A})+x_{C}\times(y_{A}-y_{B})|}{2}S△ABC=2∣xA×(yB−yC)+xB×(yC−yA)+xC×(yA−yB)∣
