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\(\overrightarrow {MN} = \overrightarrow {IN} + \overrightarrow {MI} \)

5 cm;

7 cm;

9 cm;

11 cm.

\(\overrightarrow {MA} + \overrightarrow {MB} + \overrightarrow {MC} = \overrightarrow {MG} \);    

\(\overrightarrow {MA} + \overrightarrow {MB} + \overrightarrow {MC} = 2\overrightarrow {MG} \);

\(\overrightarrow {MA} + \overrightarrow {MB} + \overrightarrow {MC} = 3\overrightarrow {MG} \);  

\(\overrightarrow {MA} + \overrightarrow {MB} + \overrightarrow {MC} = 4\overrightarrow {MG} \)

\(\overrightarrow {MB} = 3\overrightarrow {MA} \);               

\(\overrightarrow {MB} = \frac{1}{3}\overrightarrow {AB} \); 

\(\overrightarrow {AB} = 4\overrightarrow {MA} \);                

\(\overrightarrow {MB} = - 3\overrightarrow {MA} \)

\(\overrightarrow u = \left( {2; - 1} \right)\);

\(\overrightarrow u = \left( { - 2;1} \right)\);  

\(\overrightarrow u = \left( {2;1} \right)\);

\(\overrightarrow u = \left( { - 2; - 1} \right)\)

\(\overrightarrow a = \left( {1;0} \right)\) và \(\overrightarrow b = \left( {0;1} \right)\);

\(\overrightarrow u = \left( {3; - 2} \right)\) và \(\overrightarrow v = \left( {6;4} \right)\);

\(\overrightarrow i = \left( {2;3} \right)\) và \(\overrightarrow j = \left( { - 6; - 9} \right)\);                               

\(\overrightarrow c = \left( {2;3} \right)\) và \(\overrightarrow d = \left( { - 6;9} \right)\)

\(\overrightarrow a .\overrightarrow b = \left| {\overrightarrow a } \right|.\left| {\overrightarrow b } \right|.\sin \left( {\overrightarrow a ,\overrightarrow b } \right)\);

\(\overrightarrow a .\overrightarrow b = \left| {\overrightarrow a } \right|.\left| {\overrightarrow b } \right|.\cos \left( {\overrightarrow a ,\overrightarrow b } \right)\);

\(\overrightarrow a .\overrightarrow b = - \left| {\overrightarrow a } \right|.\left| {\overrightarrow b } \right|.\cos \left( {\overrightarrow a ,\overrightarrow b } \right)\);                                            

\(\overrightarrow a .\overrightarrow b = - \left| {\overrightarrow a } \right|.\left| {\overrightarrow b } \right|.\sin \left( {\overrightarrow a ,\overrightarrow b } \right)\)

\(\frac{1}{2}\);

\( - \frac{1}{2}\);

\(\frac{{\sqrt 3 }}{2}\);

\( - \frac{{\sqrt 3 }}{2}\)

\( - \frac{1}{3}\);

\(\frac{{2\sqrt 2 }}{3}\);

\(\frac{1}{3}\);

\(\frac{{\sqrt 2 }}{3}\)