303. Vector $\bar{a}=\overline{A B}$, whose length is $a=5$, forms an angle of $60^{\circ}$ with the $O x$ axis (with vector $\overline{O E}=\bar{e}$). Find the projection of this vector on the given axis (Fig. 43).

![](https://cdn.mathpix.com/cropped/2024_05_22_1b9a1c1720bae4af5bc5g-071.jpg?height=261&width=337&top_left_y=541&top_left_x=147)

Fig. 43

![](https://cdn.mathpix.com/cropped/2024_05_22_1b9a1c1720bae4af5bc5g-071.jpg?height=206&width=378&top_left_y=600&top_left_x=651)

Fig. 44
Solution. proj $\bar{a}=$ pr $-\bar{a}=a \cos \varphi=5 \cos 60^{\circ}=5 \cdot \frac{1}{2}=2.5$. 304. Vector $\bar{b}=\overline{C D}$ forms an angle of $120^{\circ}$ with the axis $O x$, which is defined by the unit vector $\bar{e}$. The length of vector $\bar{b}$ is 4. Find the projection of this vector on the axis $0 x$ (Fig. 44).

Solution. $pr_{0 x} \bar{b}=b \cos \varphi=4 \cos 120^{\circ}=4\left(-\frac{1}{2}\right)=-2$.