45. Find the scalar product of vectors $\vec{a}=(3 ; 5)$ and $\vec{b}=(-2 ; 7)$.
Solution. Here $x_{a}=3, x_{b}=-2, y_{a}=5, y_{b}=7$. Using formula (3), we get

$$
\vec{a} \vec{b}=3 \cdot(-2)+5 \cdot 7=-6+35=29
$$

46-51. Find the scalar product of the vectors: