by Cho hình lập phương $ABCD.{{A}_{1}}{{B}_{1}}{{C}_{1}}{{D}_{1}}$, đặt $\alpha =(\overrightarrow{AC},\overrightarrow{D{{C}_{1}}});\,\,\,\beta =(\overrightarrow{D{{A}_{1}}},\overrightarrow{B{{B}_{1}}});\,\,\gamma =(\overrightarrow{A{{A}_{1}}},\overrightarrow{{{C}_{1}}C})$ Khi đó: là$\alpha +\,\,\beta +\,\,\gamma $:
C. 3600
B. 3750
C. 3150
D. 2750
Hướng dẫn
$\alpha =(\overrightarrow{AC},\overrightarrow{D{{C}_{1}}})=(\overrightarrow{AC},\overrightarrow{A{{B}_{1}}})={{60}^{0}}$
$\beta =(\overrightarrow{D{{A}_{1}}},\overrightarrow{B{{B}_{1}}})=(\overrightarrow{D{{A}_{1}}},\overrightarrow{{{A}_{1}}A})={{135}^{0}}$
$\gamma =(\overrightarrow{A{{A}_{1}}},\overrightarrow{{{C}_{1}}C})=(\overrightarrow{A{{A}_{1}}},\overrightarrow{{{A}_{1}}A})={{180}^{0}}$
$\Rightarrow \alpha +\beta +\gamma ={{60}^{0}}+{{135}^{0}}+{{180}^{0}}={{375}^{0}}$
Chọn B
