3-16 할리데이 10판 솔루션 일반물리학

$$\begin{cases} \vec a=(3.0\ut{m})\hat i + (4.0\ut{m})\hat j\\ \vec b=(5 .0 \ut{m})\hat i + (-2.0 \ut{m})\hat j\\ \vec a+\vec b=\vec r \end{cases} $$
(a) $\vec r =?$ $$\vec r = \(8.0\ut{m}\)\hat i + \(2.0\ut{m}\)\hat j$$
(b)$\abs{\vec r}=?$ $$ \begin{aligned} r&=\sqrt{8^2+2^2}\\ &=2\sqrt{17}\ut{m}\\ &\approx 8.2\ut{m} \end{aligned} $$
(c)$\theta_r=?$ $$\theta_r=\tan^{-1}\(\frac{2}{8}\)=\frac{11}{24}\pi\approx0.25\ut{rad} $$