
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 that the angle between the unit vectors $\overrightarrow {e_{1}}$ and $\overrightarrow {e_{2}}$ is $\frac {π}{3}$, and the vector $\overrightarrow {a}$ = 2 $\overrightarrow {e_{1}}$ + (1 - λ) $\overrightarrow {e_{2}}$, find the value of λ such that $\overrightarrow {a}$ is perpendicular to $\overrightarrow {e_{2}}$.

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