3-12 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \vec r_a&=800\i\ut{m}\\ \vec r_b&=700\j\ut{m}\\ \vec r_c&=-300\k\ut{m}\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \Sigma \vec r &= \(800\ut{m}\)\i+\(700\ut{m}\)\j+\(-300\ut{m}\)\k\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} \Ans &= \abs{-\Sigma \vec r}\\ &=\abs{\Sigma \vec r}\\ &=\sqrt{800^2+700^2+(-300)^2}\\ &=100\sqrt{122}\ut{m}\\ &\approx 1104.536101718726\ut{m}\\ &\approx 1\times10^3\ut{m}\\ &\approx 1\ut{km}\\ \end{aligned} $$