Question

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plz help if u can

Answer 1

For two vectors defined \(\vec{a_n}=(a_1,a_2,\dots,a_n)\) and \(\vec{b_n}=(b_1,b_2,\dots,b_n)\), the dot product is defined as
\[\vec{a_n} \cdot \vec{b_n}=\sum_{1 \leq i \leq n}a_ib_i=a_1b_1+a_2b_2+\dots+a_nb_n.\]
Similarly, it is also defined
\[\vec{a_n}\cdot \vec{b_n}=|\vec{a_n}||\vec{b_n}|\cos \theta\]

Note: \(|\vec{v}|\) is the length of vector \(v\).

Answer 2

\[\cos \theta = (-6,13) . (1,0)/\sqrt{36+169}=-6/\sqrt{205}\]
so theta = arccos -6/sqrt205