Question

Помогите плизз Соч по геометрии за 1 четверть у кого был??!!

Answer 1

Ответ:

а)

$\overrightarrow{a} \overrightarrow{b} = \overrightarrow{ |a| } \times \overrightarrow{ |b| } \times \cos( \phi)$

$\overrightarrow{a} \overrightarrow{b} = 3 \times 4 \times \cos( {120}^{ \circ} ) = 12 \times ( - \frac{1}{2} ) = - 6$

b)

$(\overrightarrow{a} - 2\overrightarrow{b})(3\overrightarrow{a} + \overrightarrow{b}) = 3{\overrightarrow{a}}^{2} - 6\overrightarrow{a}\overrightarrow{b} + \overrightarrow{a}\overrightarrow{b} - 2{\overrightarrow{b}}^{2} = 3 {\overrightarrow{a}}^{2} - 5\overrightarrow{a}\overrightarrow{b} - 2 {\overrightarrow{b}}^{2}$

${\overrightarrow{a}}^{2} = {\overrightarrow{ |a| }}^{2}$

$3 \times {3}^{2} - 5 \times ( - 6) - 2 \times {4}^{2} = 27 + 30 - 32 = 25$