
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given the line $l_{1}$: $\begin{cases} x=1-2t \\ y=2+kt \end{cases}(t\text{ is a parameter})$ and the line $l_{2}$: $\begin{cases} x=s \\ y=1-2s \end{cases}(s\text{ is a parameter})$, find the value of $k$ such that $l_{1}$ and $l_{2}$ are perpendicular.

Present the answer in LaTex format: \boxed{Your answer}
user