Question

[Pham Trong Bach]

Trong không gian Oxyz, cho hai vectơ  $\stackrel{\to }{\mathrm{u}}$ = (x; y; z),  $\stackrel{\to }{\mathrm{v}}$ = (x'; y'; z') khác  $\stackrel{\to }{0}$. Khẳng định nào dưới đây sai?

A. ${\stackrel{\to }{\mathrm{u}}}^2={\mathrm{x}}^2+{\mathrm{y}}^2+{\mathrm{z}}^2$c

B.  ${\stackrel{\to }{\mathrm{u}}}^2=\stackrel{\to }{\mathrm{u}}.\stackrel{\to }{\mathrm{v}}\iff \stackrel{\to }{\mathrm{u}}=\stackrel{\to }{\mathrm{v}}$

C. $\stackrel{\to }{\mathrm{u}}-\stackrel{\to }{\mathrm{v}}=\left(\mathrm{x}-\mathrm{x}\text{'};\mathrm{y}-\mathrm{y}\text{'};\mathrm{z}-\mathrm{z}\text{'}\right)$

D. $\cos \left(\stackrel{\to }{\mathrm{u}};\stackrel{\to }{\mathrm{v}}\right)=\frac{\stackrel{\to }{\mathrm{u}}.\stackrel{\to }{\mathrm{v}}}{\stackrel{\to }{\left|\mathrm{u}\right|}.\stackrel{\to }{\left|\mathrm{v}\right|}}$

Answer 1

[Cao Minh Tâm]

Đáp án B