3-8 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \vec a&=(90.0\ut{km})\j\\ \vec b&=(35.0\ut{km})\i\\ \end{cases} $$ $$ \begin{aligned} \vec c &= \vec a + (-\vec b)\\ &=90\j-35\i\\ \end{aligned} $$ $$\ab{a}$$ $$ \begin{aligned} c&=\abs{\vec c}\\ &= \sqrt{(-35)^2+90^2}\ut{km}\\ &= 5 \sqrt{373}\ut{km}\\ &\approx 96.56603957913984\ut{km}\\ &\approx 96.6\ut{km}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} \theta_c&=\tan^{-1}\(\frac{90}{-35}\)\\ &=\bra{\pi -\tan ^{-1}\left(\cfrac{18}{7}\right)}\ut{rad}\\ &\approx 1.941687615607559\ut{rad}\\ &\approx 1.94\ut{rad}\\ \end{aligned} $$