3-13 할리데이 11판 솔루션 일반물리학

$$\begin{cases} \vec r_a&=(90.0\ut{km})\i\\ \vec r_b&=(60.0\ut{km})\j\\ \end{cases}$$ $$\begin{aligned} \vec r_s &= -\vec r_b+\vec r_a\\ &= 90\i-60\j \end{aligned}$$ $$\ab{a}$$ $$\begin{aligned} r_s &= \sqrt{90^2+60^2}\\ &= 30\sqrt{13}\ut{km}\\ &\approx 108.1665382639197\ut{km}\\ &\approx 108\ut{km}\\ \end{aligned}$$ $$\ab{b}$$ $$\begin{aligned} \theta_{x+}&=\tan^{-1}\frac{60}{90}\\ &\approx 0.5880026035475675\ut{rad}\\ &\approx 0.588\ut{rad}\\ \end{aligned}$$