3-27 할리데이 10판 솔루션 일반물리학

$$\begin{cases} \vec d_1 + \vec d_2=5\vec d_3\\ \vec d_1 - \vec d_2=3\vec d_3\\ \end{cases}$$ $$\vec d_3=2\hat i+4\hat j$$ $$\begin{cases} \vec d_1=4\vec d_3\\ \vec d_2=\vec d_3\\ \end{cases}$$
(a)$\vec d_1=?$ $$\begin{aligned} \vec d_1 =&4\vec d_3\\ =&4(2\hat i+4\hat j)\\ =&8\hat i+16\hat j \end{aligned}$$
(b)$\vec d_2=?$ $$\vec d_2 = \vec d_3 = 2\hat i+4\hat j$$