Cho hai vectơ \(\overrightarrow{a},\overrightarrow{b}\) thỏa mãn: \(\left| \overrightarrow{a} \right|=4;\left| \overrightarrow{b} \right|=3;\left| \overrightarrow{a}-\overrightarro...

* Hướng dẫn giải

\({{(\overrightarrow{a}-\overrightarrow{b})}^{2}}={{\left| \overrightarrow{a} \right|}^{2}}+{{\left| \overrightarrow{b} \right|}^{2}}-2\overrightarrow{a}.\overrightarrow{b}\Rightarrow \overrightarrow{a}.\overrightarrow{b}=\frac{9}{2}.\)

Do đó: \(\cos ~\alpha =\frac{\overrightarrow{a}.\overrightarrow{b}}{\left| \overrightarrow{a} \right|.\left| \overrightarrow{b} \right|}=\frac{3}{8}\).