A.  $\frac{a_1{a}_2+b_1{b}_2+c_1{c}_2}{\left|\stackrel{\to }{a}\right|\left|\stackrel{\to }{b}\right|}$

B.  $\frac{\left|a_1{a}_2+b_1{b}_2+c_1{c}_2\right|}{\sqrt{a_1^2+b_1^2+c_1^2}.\sqrt{a_2^2+b_2^2+c_2^2}}$

C.  $\frac{a_1{a}_2+b_1{b}_2+c_1{c}_2}{\left|\left[\stackrel{\to }{a;}\stackrel{\to }{b}\right]\right|}$

D.  $\frac{\left|a_1{a}_2+b_1{b}_2+c_1{c}_2\right|}{\left|\stackrel{\to }{a}\right|\left|\stackrel{\to }{b}\right|}$

A. $\stackrel{\to }{m}\left(-2;-4;-6\right)$

B. $\stackrel{\to }{n}\left(-2;-2;2\right)$

C. $\stackrel{\to }{p}\left(-1;-2;-3\right)$

D. $\stackrel{\to }{q}\left(3;2;1\right)$

A. $\stackrel{\to }{a}\left(2;-3;1\right)$

B. $\stackrel{\to }{b}\left(2;1;-3\right)$

C. $\stackrel{\to }{c}\left(2;-3;0\right)$

D. $\stackrel{\to }{d}\left(3;2;0\right)$

A.  $\Delta SAB$

B.  $\Delta SBD$

C.  $\Delta SCD$

D.  $\Delta SBC$

A.  ${\stackrel{\rightharpoonup }{u}}_1=\left(0;1;1\right)$

B.  ${\stackrel{\rightharpoonup }{u}}_2=\left(3;1;0\right)$

C.  ${\stackrel{\rightharpoonup }{u}}_3=\left(0;-1;1\right)$

D.  ${\stackrel{\rightharpoonup }{u}}_4=\left(3;-1;0\right)$