Notam u=i si v=j pentru a intelege mai usor.
Deoarece vectorii i+2j si 5i-4j sunt perpendiculari=>(i+2j)*( 5i-4j)=0=>
5-4ij+10ij-8=0
Am folosit faptul cunoscut ca [tex]{\overrightarrow{i}}^2=1;{\overrightarrow{j}}^2=1[/tex]
6ij=3
ij=3/6=1/2
[tex]\overrightarrow{i} \cdot \overrightarrow{j}=|\overrightarrow{i}|\cdot |\overrightarrow{j}|\cdot cos(<\overrightarrow{i},\overrightarrow{j})=cos(<\overrightarrow{i},\overrightarrow{j})= \frac{1}{2} =>\\
m(<\overrightarrow{i},\overrightarrow{j})=60^0[/tex]
