vector{BD}=vector{AD}-vector{AB}=vector{BC}-vector{AB}
vector{AC}*vector{BD}=(vector{AB}+vector{BC})*(vector{BC}-vector{AB})=
=vector{AB}*vector{BC}+vector{BC}*vector{BC}-vector{AB}*vector{AB}-vector{BC}*vector{AB}=
=|vector{AB}|*|vector{BC}|*cos 90° +|vector{BC}|*|vector{BC}|*cos0^(o)-|vector{AB}|*|vector{AB}|*cos 0^(o)-|vector{BC}|*|vector {AB}|*cos90^(o)=3*2*0+2*2*1-3*3*1-2*3*0=4-9=-5