vector{a}×vector{b}=(2 vector{p}-3 vector{q})×(5 vector{p}+vector{q})=
= применяем законы векторной [b]алгебры[/b]=
=2 vector{p}×5 vector{p}-3 vector{q}×5 vector{p} -2*vector{p}×5 vector{q}-3vector{q}×vector{q}
Так как
vector{p}×vector{p}=0
vector{q}×vector{p} = - vector{p}×vector{q}
vector{q}×vector{q}=0
-3 vector{q}×5 vector{p} =-15vector{q}× vector{p}=15 vector{p}× vector{q}
vector{a}×vector{b}=55vector{p}×vector{q}= 5*|vector{p}|*|vector{q}|*sin ∠(vector{p},vector{q})=10*2*3*sin( π/2)=60
S( параллелограмма)=60