$$\begin{align} d_1 & = \;\;\;5\hat{i} - 2\hat{j} + 4\hat{k}\\ d_2 &= -5\hat{i} + 2\hat{j} - \hat{k} \end{align}$$
What is $(d_1 + d_2)\cdot(d_1 · 2 d_2)$?
For some reason the homework problem needs an exact number answer already. When I solved it out I got $-150\hat{j} + 50\hat{i} \ldots$ I have no idea what I'm doing wrong. Someone please help!