CAIE A-Level Mathematics A2 3.7.4 Straight Lines Questions

Correct direction vector seen or implied ( $\overrightarrow{B C}=3 \mathbf{i}+3 \mathbf{j}-3 \mathbf{k}$ )
Condone $\overrightarrow{B C}=-3 \mathbf{i}-3 \mathbf{j}+3 \mathbf{k}$.

Use a correct method to form a vector equation
Allow for the RHS with no LHS.

Obtain $\mathbf{r}=5 \mathbf{i}+2 \mathbf{j}+\lambda(\mathbf{i}+\mathbf{j}-\mathbf{k})$
ISW

Must have $\mathbf{r}=\ldots$ or $\left(\begin{array}{l}x y z\end{array}\right)=\ldots$, not $l_{1}=\ldots$

Or, equivalent vector form, e.g. $\mathbf{r}=8 \mathbf{i}+5 \mathbf{j}-3 \mathbf{k}+\alpha(\mathbf{i}+\mathbf{j}-\mathbf{k})$ or $\mathbf{r}=5 \mathbf{i}+2 \mathbf{j}+\lambda(3 \mathbf{i}+3 \mathbf{j}-3 \mathbf{k})$.

Condone a column vector with i, j, k.