\(cos\left(\overrightarrow{a};\overrightarrow{b}\right)=\frac{\overrightarrow{a}.\overrightarrow{b}}{\left|\overrightarrow{a}\right|\left|\overrightarrow{b}\right|}=\frac{-1-6}{\sqrt{1+4}.\sqrt{1+9}}=-\frac{7\sqrt{2}}{10}\)
\(\Rightarrow\left(\overrightarrow{a};\overrightarrow{b}\right)\approx172^0\)