3-3 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \Delta \vec r_{0\rarr1}&=(-33\ut{m})\i\\ \Delta \vec r_{1\rarr2}&=(-33\ut{m})\j\\ \Delta \vec r_{2\rarr3}&=(35\ut{m})\k\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \Sigma \vec {r_a} &= (-33\ut{m})\i+(-33\ut{m})\j+(35\ut{m})\k\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} \Sigma \vec {r_b} &= (-33\ut{m})\i+(-33\ut{m})\j\\ r_b&=\sqrt{(-33)^2+(-33)^2}\\ &=33\sqrt{2}\ut{m}\\ &\approx 46.66904755831214\ut{m}\\ &\approx 47\ut{m}\\ \end{aligned} $$ $$\theta_{r_b}=-\frac{3\pi}{4}\ut{rad}$$