Theo Ví dụ 6 ta có: \(\overrightarrow {A'B'} = \left( { - 120;0;300} \right);\left| {\overrightarrow {A'B'} } \right| = 60\sqrt {29} cm,O'\left( {0;450;0} \right),\)\(A'\left( {240;450;0} \right)\)
Do đó, \(\overrightarrow {A'O'} = \left( { - 240;0;0} \right) \Rightarrow \left| {\overrightarrow {A'O'} } \right| = 240cm\)
Ta có: \(\cos \left( {\overrightarrow {A'B'} ;\overrightarrow {A'O'} } \right) = \frac{{\overrightarrow {A'B'} .\overrightarrow {A'O'} }}{{\left| {\overrightarrow {A'B'} } \right|.\left| {\overrightarrow {A'O'} } \right|}} = \frac{{\left( { - 120} \right)\left( { - 240} \right) + 0.0 + 300.0}}{{60\sqrt {29} .240}} = \frac{{2\sqrt {29} }}{{29}}\)
\( \Rightarrow \widehat {B'A'O'} \approx {68^0}\). Vậy \(\alpha \approx {68^0}\)