(vector{a}+2*vector{b})*(3*vector{a}-vector{c})=vector{a}*3*vector{a}+2*vector{b})*3*vector{a}-vector{a}*(vector{c}-2*vector{a}*(vector{c}=
=3*|vector{a}|*|vector{a}|*cos0 ° +2*3*|vector{a}|*3*|vector{b}|*[red]cos90 °[/red]- |vector{a}|**|vector{c}|*[red]cos90 ° [/red]-2*|vector{a}|*|vector{c}|*[red]cos90 °[/red] =
=3*y*y*1+6*0-0-2*0=[b]3y^2[/b]